To be fair I don't really hate Halo; most of my hate is directed at Halo 3 specifically. What I do hate is its effect on the FPS industry and more importantly, insane raving lunatics who do nothing but rant about how awesome the game is, who seem to just congregate in my area. (ironic thing being I play World of Warcraft and as human nature would guarantee am subject to that kind of stereotype).
And it's not that I hate people who play Halo, but I hate people who play Halo and act like dicks about it i.e. most males between the ages of 13 and 22 in this place.
And I also hate what it's done to the FPS industry. I used to be quite the avid FPS gamer, part taking in such bloody shooting shenanigans as Quake, UT, Battlefield and such, and I have played quite a number of FPS games that were released some time after Halo 3 and I have to say that after those games, the only video games I can remember playing that had any shooting in it afterwards were Mass Effect and Fallout 3.
And lastly, I tend to be biased towards FPS games anyway. I'm a total RPG gamer, having grown up with such shut-in distractions like Ultima and pen-and-paper RPGs like AD&D, especially in the days when playing AD&D was something paramount to having an altar devoted to Satan in my basement.