Underwater level hate is considered bad in so many games, not just wow. I remember the hate people had for the water temple in Ocarina of Time, or teenage mutant ninja turtles on the Nes, or Conker's Bad Fur Day, or Earthworm Jim.
People just genuinely hate water levels. I think its because of how the controls change for your character to something your not use to, plus the depth perception in some of them.
I also think, even if they actually tried to make Aquaman the video game decent, it would still have sucked balls because it was set fully underwater.