So let's get some of the preliminary stuff out of the way first:
I like Mass Effect 2 a lot. It's probably the best game I've played this year (even eclipsing Super Mario Galaxy 2, which would be impossible in any other year this gen so far). Hell, it's probably the best WRPG I've played in the past ~5 years, excepting maybe Fallout 2. Even my wife is getting into it. It's the first game I've ever gotten all Achievements in. When I end up getting a gaming PC, I may buy it a second time. It's the first game I've ever bought DLC for. It is super duper. It is a super duper game.
Just great.
I think one of te things I like most abotu it is how it differentiates so much between classes and class utility, and how each weapon in your inventory is useful in different situations. I completed my first Insanity runthrough a few days ago, which was also my first Sentinel run-through - that was a lot of fun! I will need to play through Insanity as all the other classes now, not just for the sake of being able to say I did it but also because Insanity mode in itself is a lot of fun.
Actually that's one of the things I appreciate best about this game: Insanity is tough, but it's not frustrating. I've played Insanity in the first game, too, and it's not tough but it is frustrating. When enemies take forever to kill with the best weapons but pose no greater threat the game is just tedious. ME2's Insanity avoids that pitfall. I appreciate that. I think I might start playing the game on nothihng but Insanity.