If you finished Mass Effect, your gonna get Mass Effect 2, that's a fact !
I considered the first game to be innovative because a few years back when I played the "Knights of the old Republic" series (and I absolutely loved it), I was thinking: "how cool would it be to have a game with such complex RPG elements and a fast paced gameplay ?". Maybe Mass Effect isn't the perfect fast paced 3rd person shooter out there (or maybe it is), but it's damn good and most of all it's taking large steps to my dream-game.
I really enjoyed playing Mass Effect 2 but when I finished it I was like "You gotta be kidding me... PLEASE !!! Just a few more hours of gameplay !!!!". One thing I didn't like though, the main plot was pretty damn short, if you don't do all your companion's side missions then your gonna be pretty damn pissed off and gonna restart the game to play it thoroughly.
Of course the writing is awesome, those Bioware dudes probably have a bunch of washed up writers locked up in a basement, feeding them crappy food and cheap wine, so they can feed of their work, work blooming from the pain of doomed failure, you strive to get out a few decent material and you end up trying to outsmart a bunch of pixels, on a website where nobody recognizes you, asking yourself where did you go wrong.... what was I talking about ?
Anyway, If you want to play Mass Effect 2, I suggest you get Mass Effect first and if you like it THEN get the second part.