There's three kinds of hate that WoW gets - from people who've never or hardly played it, from people who've played it and currently don't, and from its current players. Which one are you referring to?
People who've never or hardly played it - that's been hashed out pretty well in the thread. There's the stereotyping, the "no life" labeling, the hate of the pervasiveness of it into gaming culture, and the like. Whether or not that is legitimate or informed, it's there, and will always be there.
People who've played it and currently don't are another breed. I'm the "Number One" role (minus the beard and hand wringing Riker usually does) at a Warhammer Online fansite, and we deal every day with people who mindlessly bash on WoW rather than have a good discussion about the differences. I'm an ex-WoW player, having gone all the way to Naxxramas pre-TBC, and I dislike the game for my own reasons. Others do as well. That kind of hate is also rational or irrational depending on the argument.
Then there's the people who currently play it. I honestly think the WoW-bashing that occurs from people who don't play the game pales in comparison to the angst, ranting, and rage that happens daily on WoW's own forums from people who currently play the game. The amount of things that upset a player can range from something as small as a bonus item or chance encounter all the way to the highest-end gear and class balance issues. For all the attacking people do on WoW from outside its halls, its current players sometimes seem to hate the game more than they do (but unfortunately can't tear themselves away from it).
For me, my main gripe with WoW extends to my main gripe with a lot of Blizzard titles - they're "McDonaldized" content, geared towards the lowest common denominator, worship the great subscriber number over unique and meaningful game design, and make things terribly generic so that anyone can pick up and play the game. The kind of widespread appeal that Blizzard creates may be seen as a positive to some, but to me, it's a negative, because Frankensteining the best of mechanics from other titles into a package meant for everyone to play doesn't always translate to innovative, interesting design, just recycled. And that's especially apparent in WoW, where the design is geared towards keeping someone who is an addict hooked and forcing them to play constantly to get ahead of the curve. I'm sure this isn't laziness and Blizzard is dedicated to high-quality content. They are to be commended for creating an MMO with such immense appeal. It's just not really a translation into a good game in my opinion.
In essence, WoW and Blizzard don't deserve some of the hate they get, but the design of the game as it stands doesn't discourage that kind of burning hatred, either.
