You get used to any style after a while. They are all different. I've never really had a problem with WoW's style. It is cartoony, but then some of you may remember that when DAoC was first released, its graphics were criticised as being cartoony too.
I always wonder whether the WoW style of graphics was necessary to meet some technical consideration. When you move around the WoW world, you will find that loading screens are rare and never take long. Will be interesting to see if this is the same in Warhammer. I hate loading screens. It's like someone switching the movie off for 30 secs every few minutes.
I agree with Cryn, WoW's graphical engine is deliberately last generation, It caters for a much wider audience when the playing requirements are so low, heck it plays on my fathers 1.8 Athlon xp, with 512 mb of ram & a 5200fx video card I tried 3 others swg, eq2 & Daoc, unsurprisingly I had trouble playing all 3...
Right there you have cornered a huge market as not everyone has a top of the range flying games machine.
I know though there is much more to WoW's success than just its graphic style, but personally I couldn't get into WoW I have had a much more pleasurable experience playing everquest 2, but perhaps I have deviated so far from the topic I'll actually shut up now...