Frankly, I liked Mass Effect 1 much more in spite of its weaker graphics, and quite a few others did too.
And it's not so much that "Mass Effect 2" is a "good game", but that the trilogy as a whole (the third one comes out in about half a year) is good, with what you do in the first influencing what you get in the second (by importing the end-of-ME1 savegame) and the second one doing the same for the third one.
Mass Effect 3 is supposed to conclude the big epic Shepherd-vs-Reapers story.
It's also not just the game, it's the whole setting - there's three books out (and a fourth one on the way), which are arguably decent (the first one is a prequel to ME1 and explains a few things, the second one happens between ME1 and ME2 and is actually briefly referenced in ME2, the third one happens after ME2 and has as a strong prerequisite something you did during ME2), there are some other more casual games, some comic strips if memory serves right.
But yeah, ME2 all on its own, without everything else... not really that great at all.