It's pretty amazing. Definitely a wonderfully created and well-written sci-fi. The only thing that irks me is how the Asari look just like humans and how they can breed with any alien. It really hurts the scientific part of my brain, but then I've always been more partial to hard sci-fi (aliens that look identical to humans only with bigger foreheads make me want to cut myself). Otherwise though it is a very well conceived story with a nicely fleshed out world. And boy do I love my female Vanguard!
"Believe nothing, no matter where you've read it or who has said it, not even if I have said it, unless it agrees with your own reason and your own common sense." -Buddha