Late last year I, at long last, played Mass Effect when the trilogy box was released for the PS3. (Here's the review blog post I wrote.) After finishing it, I, naturally, immediately started playing Mass Effect 2. However, stuff happened (trips, illnesses etc.), and I got sidetracked for several months. Last night, however, I finally finished my playthrough. And it was... fairly awesome.
If you're not familiar with Mass Effect, I suggest you start with my post about the first game. Much of what I say about it is also true for the second. In this post I'll focus mostly on the differences, of which there were some.
I don't want to say too much about the plot, in case of spoilers. Suffice to say that commander Shepard is still around, the Reapers are still out there, and the authorities still aren't taking the threat seriously. One interesting feature of the trilogy is that you can import your save file from the previous game. Choices you made earlier will have an effect on events in this game as well.
Gameplay remains quite similar. However, there seems to be a slight shift in focus away from RPG elements towards tactical combat. Most notably the inventory management, which played a large role in the first game, has been basically removed entirely. You still get equipment upgrades, but these are one-off things which usually benefit your entire team from that point on. (This, I think, was probably a good move, since managing the upgrades in ME1 was something of a hassle.) The characters also have fewer talents to level up.
Meanwhile, the role of cover in combat is emphasized even more than in the first game. They have also limited ammunition, which may force you to switch weapons should you happen to run out (though this happened relatively rarely for me). Exploration has also been changed somewhat. Instead of just hitting a button, you now have to manually scan planet surfaces in a mini-game. (Which, honestly, is pretty boring.) The storytelling and the game's dialogue system, on the other hand, remain practically unchanged, and still play a crucial role.
Visually the game has probably improved a little from the first one. It's still maybe not one of the most detailed around, but the graphics worked well enough for me. (The game also felt considerably less buggy than the port of the first game.) If there was one disappointment, it was maybe the way certain 'hub' locations were presented, particularly Citadel, which just felt much more confined and less impressive than in the first game.
ME2 is a pretty lengthy game, too. I finished ME1 in under 30 hours, whereas this time the game's clock read close to 50 hours. Even though I did relatively little additional exploration, maybe even less than in the first game (the game still doesn't really give enough incentive for it), I probably played through a few more optional missions. Many of the game's missions are related to characters on your team, which made them a little more interesting than much of the optional stuff in ME1. The trilogy box version also includes several missions originally released as DLC, which easily added maybe ten hours of play, and were, actually, pretty cool and interesting.