Wow is good because it runs smoothly. Many other games are jerkish, like War. Sure I could buy better hardware, but hey, I already bought a machine, I don't want to hunt additional stuff for it to work. Some people go after good hardware, but I guess I stick to Wow then.
I really hate bugs and annoying things. War has good ideas, but I hate it for the bugs and general graphics. Wow has larger icons and better user interface, though War has more stuff, but harder to see. My screen is not set to 100% bright even. But in general, bugs are what I hate most.
Also the user interface should be usable, not "usable". Some games try to max usability, but fail miserably and the result is a mess. In Wow the chat window doesn't move if I rotate the view on it. In War the chat window moved instead of the view rotating when I tried to rotate view on the chat window. In Wow nothing happened if I tried to rotate view on the edge of the chat window. That happened surprisingly often, and I hated it. In War the whole chat window is a problem zone (unless they have fixed it by now).
Good old games didn't have much bugs:
Switchblade II