The reason that there's a lot of hate is because people are starting to realize that the choices they have to choose from is becoming more and more stagnate.
You can only take to Call of Duty series so far before it descends into an unaware self parody and repetition, same with Halo, Quake, and sadly enough from what was shown from New Vegas, the Fallout franchise as well. All of these games have become more like brands put on a game than an attempt to extend an actual storyline.
Do you actually believe that these series are so good that people should keep trying to retell and rehash the same stories over and over again? Is Call of Duty so good that that studio should spend all that effort, all that man power, trying to keep little more than a name alive? Even people who aren't well spoken can see this in some way and that is why they flame the Modern Warfare 3 threads.