Mass Effect 2 is good stuff, but it does get me confused every now and then since I haven't played the first game. The first two hours were spent mostly on figuring out WTF is going on, who is who and what they do, occasionally it throws in some new dude(ette)s who you are apparently supposed to know, which makes some strange conversations since I'm not entirely sure how to talk to them.
But other than that, well worth the time. Plenty of talky talk, colorful characters, mostly enjoyable combat ( face it, smashing a warp blast right into someone's jaw IS satisfying ) and nice story.
+1 cookie from me.