Every game has fans and detractors. Halo currently has a larger base of fans than almost any other game. Just as every physical action has an equal and opposite reaction, so does every popularity have an equal and opposite backlash.
Detractors of a game tend to be more vocal the more they feel they are in the minority. For example, crappy licensed games such as Open Season and Transformers are generally regarded as bad games, so the people who dislike them (i.e. nearly everyone) don't bother to mention them. Final Fantasy and Gears of War are both game series that are quite popular but somewhat divisive, so people who dislike either one will put some effort into criticising them, but they won't go over the top because they know a lot of people agree with their opinion. Halo is regarded as a good game by the majority of gamers (based on reviews and the non-Escapist population), so the people who don't enjoy it feel like they need to shout down the teeming masses of those who do, whether they say it's outright bad or just "overrated".
The Escapist seems to have a disproportionate share of people who dislike Halo and want to tell everyone about it. I don't know why this is. It might be because Zero Punctuation attracts the sort of people to the site who like to criticise things and attack things that they don't personally enjoy. That's just a theory, though.
Interestingly, many of the people who passionately criticise Halo don't have anything really bad to say about it. A typical complaint will simply say "I hated it" and either give no reason or point to aspects of the game that are common to many other games, if not totally standard for the genre. Examples include: the subtle auto-aiming, the generic story, the space marine protagonist, the "easiness" of the game (ignoring the ability to set the difficulty setting), the regenerating health (although didn't bother them in COD4) and so on. Others, such as NDWolfwood5268, claim that the first game was good but later games in the series are total crap because they only improved on it a little bit and didn't add many new features; anyone who can explain that logic is free to try.
A lot of criticism also centres on the story, often with reference to the superiority of story in games such as Half-Life 2. These people apparently have no problem with the hundreds of other games that have a more minimal story than Halo. They are also often not willing to even consider the quality of the multiplayer experience, although they seem fine with Team Fortress 2.
