The fact that Bioware call it a RPG makes me laugh, but if you like Gears of War "cover style" games you'll probably love it.
For me, it paled in comparison to the vast majority of releases Bioware have made (and pales further when compared to Obsidians efforts) but I'm in a very small minority!
Don't get me wrong, I don't think it's a bad game, I just don't think it's deserving of unilateral praise it's getting accross the board.
KOTOR2 is most certainly a better Scifi RPG despite it's many flaws.
There are virtually NO interesting NPC's at all in Mass effect, including party members
. The only characters that I found remotely engaging were Wrex (because of the Krogan cloning planet) and the human ambassador to the council (mainly because of the ending that I chose).
There was just so little depth to the characters that it was unreal, KOTOR 2, despite it's faults, did the characters very well.
You had a force user wanting to destroy the force, a droid that wanted to bring order to the galaxy via the republic, but was willing to be as evil as hell to do so, an apprentice to one of the main baddies you need to fight, an old solider you were responsible for in a past war that both hates and admires you at the same time, a wookie tormented by life oaths so in order to be an evil git you subject him via saving his life etc... The list goes on. In Mass Effect, it doesn't. The characters are so one dimensional it's almost scary.
With this in mind, you very rarely feel attached to any of the characters so when the game asks you to choose someone to sacrifice for the cause, the game may as well ask you to flip a coin - you probably don't care, as they're all the same generic "grizzled" solider character you've been made familiar with through most RPG's
The baddies are the same deal really, Saren just doesn't cut the mustard, you convince him on several occasions what an idiot he is, I managed to convince him to blow his brains out at the end and at no point did I really feel like he was a convincing evil so and so. His reasoning for what he was doing was so flawed and generic that you could probably finish his lines for him. On top of that, how many times are we gonna get the race of beings that only desire to destroy all life "just for the hell of it."
ME2 suffers from exactly the same problems.
Characters are ultimately the way in which a story is told, if you don't give them flesh on their bones then the story won't be portrayed in an interesting way.
Bioware games, much like Bethesda games, don't seem to get a fair review until the hype dies down 6 months later (Ie Oblivion went from being "wow it's perfect" to "actually no, it's nowhere near.")
7.5/10 for me.
If you enjoyed ME2 as an RPG then I'd advise you to look at System Shock 2, Deus Ex, KOTOR2 and Fallout 3.
If you're after a "proper" RPG, I'd look at Planescape Torment, Vampire Bloodlines, Arcanum, Mask of the Betrayer, Baldurs Gate 2, Fallout 1 + 2 and The Witcher