So why does everyone hate him?
Firstly, I have read the books. I know it's sexist, and I apologize, but at one point he kills an unconscious woman just because he can. That's one of those moral event horizon thingies, and I just wanted to see him dead afterwards. But no, he magically survives the encounter with Anderson, goes on to kill another major character from the books (the autistic biotics experiment, with a toothbrush).
Then, in the game, he induces cut-scene incompetence in any encounter with Shepard - I'm an infiltrator and brought Garrus for good measure... so why can't I snipe him? No, I'm sure the Predator pistol of b*tchslap is much better idea...
That's just crappy writing - you beat him at every turn (even when he brings a gunship for support), but he still "wins" every encounter. That's just not fun to play.