Bioware at it's best, there is no equal.
The volume of the dialog, and paths you can choose is mind blowing. The humor is there as well, just listening to a couple of NPCs chatting will crack you up at times. The level of immersion into the Mass Effect 2 world is intoxicating, I have other games backed up, and neglected because i'm on my 3rd run through of this fantastic game, thinking about a fourth!
When you think about games, even great games, you can always see room for improvement, but improving on ME2? I can't think of anything segment that needs it. If you don't own this game, you are really missing out on an amazing gaming experience.
Mass Effect 2 is a "must own" tittle, if you don't have it, get off your lazy ass, and go get it foo!