Thanks to local stores breaking the street date of ME2 by several days, I've put about 20 hours into the sequel already.  It's a welcome reprieve from the shit I'm dealing with in the real world, and does a great many things better than its predecessor.  I feel that a lot of the RPG-centric folks will dislike it to a degree because it does lean hard on the side of shooters, doing away with the traditional inventory and being able to individually outfit crew members with armor or upgrades.

To this end they've accomplished much: the animations are considerably better, from leg shots staggering enemies to the great freezing effects of cryo ammunition (which is a power, not an item by the way) and a much improved cover system.  All of the weapons generally feel more substantial than their equivalents in the first game, and despite my intial resistence to lugging around a heavy weapon some of them are pretty damned impressive.  For the most part your squadmate AI has improved greatly, though you still have cases where the idiots just won't take cover and get themselves shot up.  Luckily, as if to balance that out, their autonomous power/ability usage is considerably more intelligent than before.  It feels to me more like being the main guy in a three man (or woman) team rather than being the only one with two dead weights following you that occasionally send a few bullets toward the enemy.

The dialog system is back in its full glory, and improvements have been made there too.  Gone are the generic "character looks left and exits stage" animations at the end of conversations.  There is a much greater variety in everything conversation related and unlike a certain other action-RPG making developer/publisher I can think of there are more than half a dozen voice actors.  Everything cinematic that people loved about the first game is taken to the next step, to practically film quality.  In many respects it goes beyond that, simply because the media is interactive.  All of your crew members have deep backstories which drive side-missions used to secure their loyalty and unlock new powers, only available while they remain loyal.

It'll probably sound strange for me to say this, considering some of my favorite games generally involve killing hordes of zombies or each other over the internet...but the single most memorable thing thus far in 20 hours of game is emotion.  I can't really express how stunning some of the conversations in this game are due to the sheer intensity of the dialog and the brilliant voice acting that goes with it.  I think it can be considered an achievement that Mass Effect 2 is possibly the first game to believably pull off tears in digital form.  Screenshots do no justice.

Bottom line?  It's more shooter, but the power of the original game is there and then some.  Though the PC copy has some issues in the UI, it's still a solid co-development instead of a shitty port.  Mass Effect 2 is about as close to a must-buy as I can recommend.