However, the real meat of the expansion is in the new defensive starbases. These contraptions, about the size of a full-blown moon when compared with your planets, are the core of all Entrenchment is about. Other defensive structures can delay a fleet long enough for help to come, but a properly equipped starbase can literally cripple a fleet on its own and force if to retreat... if it doesn't wipe it out completely.
That is not to say they are invulnerable, however, as any properly outfitted fleet can be the end of a starbase, especially thanks to the new “anti-structure” cruisers, such as the TEC's Ogrov torpedo cruiser, a cruiser-sized weapon platform firing structure-mashing torpedoes the size of a fullblown frigate from a distance that outrange most defensive orbital weapons.
However, most starbase will still be a though foe to tackle for the unprepared. With armor and health that put most capital ships to shame, they are very difficult to get rid of. And not only that, but these defensive stations can also be upgraded to get even tougher armor or weaponry, most fleets will have a hard time to put one down.
And these upgrades is where the starbase truly shines, as ultimately their use will is defined by how their owner decides to customizes them thanks to the sheer amount of different upgrade you wishes to give them, each races having some capacities unique to themselves.
Need to build a fleet of ships on some far-away world? Then upgrade the local starbase with production hangars that will permit them to produces frigates and cruisers. When upgrade to the latest production facilities, they will even do that job faster than any frigate construction yards orbiting a planet. And with the ability to deploy a starbase anywhere you want (even on non-colonizable sectors) thanks to the new construction cruisers, such a starbase can be placed close to enemy sectors to become the starting point of an invasion fleet.
Or, if you /really/ want to defend a sector, such as your capital planet, you can place a starbase there and upgrade it with new weaponry, armor, and a strikecraft hangar that, once fully upgraded, can almost fills any planet's needs for defense fighters and bombers.
Then, come the specialties uniques to all races, such as the Advent's capacity to turn their starbase into a culture node, or the Vasari's starbases' mobility, which permits to chase the enemy fleet across a gravity well, denying him of the advantage of merely moving out of weapon's range, starbase can become inherent to a strategy.
That is not to say they are the answer to everything. They remain first and foremost a defensive structure, locked down within a single sector. And a costly defensive measure at that.
The price of most starbases, even without any upgrades, makes capital ships looks affordable in comparison. And their upgrade alones carry a most hefty of cost to get, requiring anyone thinking of building starbases to have an excellent economy prior to undertaking the endeavor. Still, for what they cost, their use if more than worth it.

Graphics

Being a micro-expansion, Entrenchment doesn't bring that much in the graphics department. Still, one has to admit the new starbases are quite something to look at, from the Imposing TEC starbases, to the mobile “moons” of the Vasari without forgetting the sleek and elegant Advent bases. All of them are good looking in their own way, adding to the visual designs and aesthetics of their respective races. I, for one, did love seeing the concept art behind them, from concept artist IgnusDei ( http://ignusdei.deviantart.com/ to go and see some of the pieces he did for Sins of a Solar Empire, along with some other pieces of art ).

Final note

All in all, Entrenchment is a very nice expansion. Though at first sight the content it adds might seems minimal, in practices it can literally change the flow and strategies of a game thanks to the new massive Starbase, the heroes of this expansion. Entrenchment truly does deserve its name, for it literally manages to bring the experiences of trench and siege warfare to the interstellar level.
It would be a shame for fans of Sins of a Solar Empire to pass by this one without buying it, when there are so many other so-called micro-expansions that asks you to pay even more money for less content than what Entrenchment brings you.