As in all games, MMO or otherwise, Warriors are my least favorite. I am more fond of classes that can heal, or bring something more to the table than a sword and board. I might make a Charr one to see if I am right, but what I've seen in videos and read so far, it is the least interesting to me. Even if it is fun, I am sure my Guardian or Necromancer will be even more so.
Berserkers and Knights are just specifications for warriors, which is too limiting.
This; a berserker or knight is basically just a warrior specialized a certain way, in WoW for example, Berserker = fury warrior, Knight = Arms warrior. Warriors allows for a wide range of play allowing them to add a broader range of skills and playstyles to the class instead of being stuck in one. Do you want to be that warrior who protects the weak? the one who goes into battle swinging axes drunk and shirtless? Or the master tactician? Well instead of three separate classes you can choose to be any one of these things.