I finished Mass Effect 2. In a word, awesome.
For those who complained about combat in the last game, it's far superior. For those who didn't like the Mako, it's gone, replaced with beautiful side quests on alien worlds. It's two discs for a reason (the reason? Epicness).
There were some serious decisions to be made at the end, for anyone who is wondering. I'm not sure I fully like the ones I made in this one. Most, yeah, but this is a darker game than the first. All those Paragon or Renegade points will help you a lot, but it won't help you with the decision at the end.
Dialogue is top notch, like before. This game is so far ahead of the game when it comes to RPGs, surpassing Bioware's Dragon Age, by far. It's simply far more engrossing to hear Shepard speak all your dialogue. At one side mission, you go to a trial. I chose a Charm dialogue option, and Shepard literally made a rousing speech, with back and forth, to show the character's innocence. You simply don't get the same seamless effect with reading through lists of dialogue. The interrupt system was also employed effectively.
As a bridge in a trilogy, the main plot suffered... a little. It wasn't as earth-shattering than the first game, but the revelations were cool, and I honestly didn't see the final twist coming. I don't know if it's better or worse than the first game, story-wise, it's merely different. There's a lot more time spent with characters, and they are all fascinating. So, its plot was propped from the excellent characters, and the excellent writing. I laughed out loud to dialogue multiple times. If you know your sci-fi, there are some really hilarious homages which I know Bioware put in intentionally. (Mild enthusiasm: You've never seen Hamlet until it is performed by an all-elcor cast.) Bioware is a genius. Savor the little details; they are great.
Needless to say, if you were worried about not having your romantic interest from the first game join your party, as Bioware stated pre-release... Don't. Seriously, don't worry about it. The game's tone is darker. If you liked your first romantic interest, you really don't want him/her dying. You're doing them a favor.
Anyways, if you haven't played it, you need to. I've been playing it more or less for forty hours since 7pm on Friday night. My eyes are bloodshot from awesome.