I have never played games like Doom 3 before, so when I first started playing the game it was real cool and somewhat scary! Obviously having not played doom 1 & 2 I cannot compare them to Doom 3. But I like the graphics and I like the way the game plays out the storyline. For me it was good to have some time running around shooting at demons before being introduced to new types of demons and taking time out to read about them on the pda in the game. I liked that the game was dark! Sitting in my room with the lights out, the sound pretty high getting the effect was really great. I found myself jumping when bodies would fly or move randomly and when it goes real dark and you see red flashing lights and demon laughter then ........BOOM!......... something attacks you from behind or from above really made the game all that better to play. True, some people were right when they said "some parts of the station all look the same" (which is true in nearly every game Halo, Half Life, Farcry, Bloodrayne, Unreal, etc!!!) and it would have been pretty repetitive, but half way through the game you finds yourself in hell (that was fun!) giving you a break from offices and corridors. some have said Doom 3 is short, well if your going to try play the game constantly for 24 hours, it will be wont it!!! the game is designed 2 b played at night giving a beta creepy effect, you don't have to play continuously. I know some gamers like to play games continuously (which will make the game short!) but I found the game much more fun playing in bits, I found myself looking forward to what was coming next and what other types of demons there are. I don't know why people were complaining about it. I'm still playing a couple of hours a night and its still a great game and I'm still on the edge of my seat. 
Happy Gaming =]

It's taken me a while to write this, so apologies. I bought the expansion pack Doom 3 Resurrection ages ago. Wow its amazing! You clear levels and then get a different boss at the end of each one. It's still as spooky as Doom 3. You get different maps and some different gear. Its well worth the buy and the time.
Happy Gaming =]