Personally, Mass Effect 1 wasn't too much of an appeal to myself. I felt like it was very, very RPG-feely. And since i'm not a huge fan of RPG games, I didn't really enjoy it.
Mass Effect 2 is totally amazing. Bioware really hit the nail on the head in ME2. The campaign story was awesome, it was addicting, all around a fun game.
Mass Effect 3 is pretty good so far. I have a few complaints for it though. Something a bit weird is the frame rate during cut-scenes are pretty low for whatever reason. Mass Effect 3 also just feels like a HUGE DLC pack for Mass Effect 2.
Don't get me wrong, ME3 is totally awesome. It just might be a tad bit too similar to ME2 :P