It's best to start out by stating two facts.
First off - Bioware is one of those rare game companies that are almost entirely reliable. In fact, only Blizzard are comparable in terms of consistency. Which means that their games are almost always - Neverwinter Nights offered a fairly poor single player experience - fantastic... it's something gamers appreciate and something that is incredibly rare.
The first thing to point out is - Mass Effect doesn't optimises your configuration... initially this made it seem as if it was an uber whore, putting Sanginus Nox - a machine that managed to cope admirably with Crysis - into jerk city... Fortunately this turned out to be because the audio was running on software alone... once that was sorted the game ran just fine. Also, your experience with the DRM may vary... but as usual, it seems to have been more of an impediment to legitimate players than pirates... Clearly it's asking too much for publishers to learn lessons.
The premise of Mass Effect is fairly standard - you're trying to stop the run of the mill bad guy from destroying the galaxy. It's more elaborate - naturally - but it's hard to go on without spoiling it. Although, the story doesn't develop so much as it is spilled out by various bouts of exposition. This is probably one of the main flaws of the game... you never really get the feeling the plot is developing, you just blunder from one plot update to another. Not only that but if you've played Knights of The Old Republic, there are some definite similarities. Although, that said - while the premise it uses is somewhat cliche, the universe it's set in is definitely interesting and is probably one of the strongest aspects of the game.
It's inaccurate to dub this game an RPG... at least in the traditional sense... the game is more Deus Ex than KOTOR in that there's no RPG style tick-tock round combat - which KOTOR contained... albeit in a rather unobtrusive manner. Although, it's third person and of course, you can pause to issue orders to your squad. At points the game actually manages to give you what are fairly realistic firefights. Which is to say, unlike in an RPG when range attacks will be exchanged briefly before everyone runs at one another to get within melee range - if you break cover to try and run up and bash people on the head here or just stand out in the open, you're probably going to end up dead and unlike KOTOR, if your main character dies in a fight - game over. This can be a little irksome but at least makes sense as the control you have over your squad mates is fairly loose. Which can become frustrating when they stand in the middle of a room and die, overall it's fairly passable - although the enemy AI does occasionally have a propensity to stop hiding and just run at you or try and circle strafe at point blank range.
The combat itself has configurable difficulty, ranging from the hand holding "point in the general direction of something and it falls over dead" to "hardcore gamers only", presumably the options are there so that those not au fait with more realistic, less tick tock combat are not frightened by a game that does occasionally require reasonable accuracy and reflex - at least on the higher settings. Of course, the options included allow you to determine whether the combat is a formality or a big part of the game. Regardless, it's a fairly intuitive system and barring the occasional idiocy of your squad mates it's quite enjoyable. As you'd expect, weapons and armour can be upgraded and there are variety of items out there - some better than others. Rather vexingly, weapon skills are class specific - so, if you're a Vanguard, no matter how good you get, you'll never be able to skill up with an assault rifle. You can still use one but even crouching down on a single shot basis with no wind, you'll be lucky to hit the broad side of a moon. Also, there's a notable absence of melee weapons... you can run up and pistol whip people but no discernible melee weapons but then given the combat dynamics of the game, they'd probably be the equivalent of suicide for all but the most heavily armoured and shielded individuals.
An interesting aspect of the weapons are that you can buy licenses. Basically this means that there are some merchants who will sell you a license and that the vendor on the Normandy can then stock that brand of weapons or such - as there are several companies that produce weapons. It's nothing huge, just an interesting touch that adds something for the more obsessive player to do... although, some of the sidequests would surely provide just as much of that.
Romances and party subplots are a little thin on the ground - but then when you take into account the fact that the game is so short, that's not surprising but more on that later - and on the first play through, despite trying to pursue a relationship with the blue chick, randomly the human girl ended up jumping Sheppard's bones... with no real warning... so, it was rather... hollow, not at all like the romance options in KOTOR or Baldur's Gate 2 where there could be lengthy and sometimes tricky romances. The sex scene that Fox News decided to start foaming at the mouth at is laughable - you're likely to see raunchier things in shampoo commercials. All-in-all, this aspect felt somewhat tacked on... a mere concession to the Bioware tradition. It's not bad but it feels so woefully underdeveloped and for one of the love interests to throw herself at you when you've not really pursued any of the romantic interest options is just poor.
Speaking of tacked on there are two other aspects of the game which feel rather incongruous in this way... the most obvious is the Mako. Basically, when you go to a planet that isn't in the main plot - you get dropped in the Mako... basically a magical tank that never gets flipped over and can go up almost vertical inclines. It's not bad... in fact, sometimes driving around and blowing up enemies in this fashion is actually pretty fun but sometimes bumping around on the uneven terrain of a planet, hoping to find stuff - ore deposits only show up on your radar, not the overview map. It's really the driving around on the uninteresting planets going from point A to B over abysmal terrain that proves to be irksome. In fact it feels as if they've tried to increase the action quotient with this aspect of the game as there are several main plot missions where you're essentially forced to hop in the Mako and drive along a preset route. It's just something that feels slightly out of place in the game but that for whatever reason Bioware shrugged and decided they'd stuck it in there, they might as well make use of it. It's not bad but it just gets boring after a while.
The other is the irritating subgame that you have to play EVERY time you want to try and open a locker or pick up an artifact or even survey minerals. Essentially you have to move an arrow to the centre of a circle in 15 seconds - although, hacking skills are still relevant and if you've gone someone that isn't imbued with the right skills, you should prepare for just about every box to be unhackable within relatively short order... not that it matters. Regardless, it's just a somewhat irritating and pointless endeavour that doesn't add anything to the game except a level of irritation. Fortunately you are sometimes afforded the chance to simply use "omni-gel".
Unlike KOTOR, Bioware seem to have deliberately made this game more console friendly. You don't have a proper inventory... just a big long list of the stuff you've got... also, no searching bodies for loot... although, that's a nice time saver... the level up situation is a lot simpler than previous games Bioware games too. Given the combat logistics, it's not surprising the D&D rules are out the window. There are no attributes like strength, intelligence etc. to mess around with. All you've got are the various skills your class has, some need to be unlocked but beyond getting a specialisation - these are the skills that will have to do you for the entire game.
The rogue equivalents in this game basically get a bunch of tech related stuff that lets them mess with other people. Affect the overheat of their weapons, hack AI and so on... the caster equivalent use mass effect things - which equate to toss people around, mostly... which NEVER stops being hilarious to watch. Plus it tends to render groups of enemies all floaty and useless... and the DoT warp allows you to bypass shields... which is a real bonus with some enemies.
And of course, what kind of Bioware game would it be without the aspect of morality? As with previous Bioware titles, you are often presented with opportunities to act nobly, selfishly or just indifferently. At times, conflict can be entirely circumvented by the correct dialogue and at other times, one can force conflict with a suitably belligerent attitude and even the most satisfying - cold blooded murder in public for your own gains.
An example - choosing the Earth background means at some point your character will be approached by someone from a gang you used to run with. He asks you to talk to a turian who is has a fellow gang member in custody. Naturally you can either choose at this point to take the mission or tell the guy to get lost. When you proceed to the turian, you can then either try and persuade him to free the criminal or tell him the gang member's plan. The latter prompts the gang member to arrive at which point you literally have the option to just turn around and shoot him in the head to prevent him from spreading stories of your somewhat chequered past. So, essentially all the depth that you'd expect... one very slight difference is that the dialogue responses are not word for word what will be said but rather the general tone but as you'd expect the choices you make mould the game and there can be significantly different outcomes given your responses.
The most vexing thing about the game is... just as things seem to be gaining pace... it's over. The main missions and a good portion of the sidequests can be be completed in a little over 20 hours... naturally, there are more sidequests for those inclined to go looking - there are several systems that you never have any cause to go to which are there essentially for the purposes of additional missions. The main plot breaks into essentially 7 missions - naturally, you can just play through them at any point - but it's not exactly compelling. There's no sense of uncovering a mystery like there was in KOTOR - you fight your way through the requisite bad guys and then are generally treated to a few steaming portions of plot exposition. In fact, several times this plot exposition is really only tangential to the main plot and so there's something of a feeling that you're really only seeing the development of the main story in the final act where it's essentially threeish exposition fests which explain something that any astute player will probably have clocked pretty soon into the game.
The fact that the story itself is built upon sci-fi cliche upon sci-fi cliche doesn't help. Ok, there are some aspects of sci-fi that are just so cool that people can't help but use them over and over but surely a different spin could have been put on things... compared to compelling yarns that Bioware has done before this one comes off as too short and too shallow. KOTOR gave you pretty extensive dialogue options with your crew and while there's some banter in the levels, the interaction never really gives you any feeling of true depth and there are hardly any of the spontaneous NPC on NPC interactions of those games - a little talking in lifts but that's about it...
But then, given the games length - that hardly seems surprising... and it really is to its detriment. While Mass Effect certainly does a good job of hitting the ground running the main plot missions don't feel particularly pressing until the last act and then when there's all that momentum built up - the credits roll. Now, as mentioned above - there is the option of galactic exploration, fly to clusters and get assigned missions when you get there, find a bunch of things etc. There's no doubt that there are many more hours in the game for someone who fastidiously WANTS to 100% the game... but surely if the game was better designed then these wouldn't have required you to go somewhere "just because"... and it seems fair to comment that Mass Effect WAS advertised as epic and seems to think of itself as epic... the potential was there but it's never realised and the fact that this is apparently being stretched across a trilogy seems to be a concession to EA's lust for profits over quality games rather than any sort of vision of Bioware.
In the final analysis, it's a fun game that can be enjoyed by RPGers and action game fans in roughly equal measure - although RPG fans may be left somewhat disappointed by the rather shallow dynamics - and while it's good, it feels as if it was really just getting started. No sooner have you got into the swing of things than it's over - oh, naturally there's the replay value of going through it again, looking for those random sidequests, playing it as evil instead of good, etc. but it's never really the same the second time through and given that this game is from Bioware, it's rather disappointing that it's all over so soon. Which is, in it's way - a backhanded compliment... but then, when you're forking over your cash for a game, you probably want something that will take you more than a few days of hard gaming to burn through, don't you? In fairness, still better value than going to see a film and it is enjoyable, pretty and interesting... it's just a shame that it's (relatively) shallow and short... let's all hope that Bioware hasn't sold their soul to the devil by working with EA...