I want to second this.
Actually, to expand upon this.
Water in 2D Mario? Lame.
Water in 3D Mario? Annoying.
Water in Zelda? Super Shitty.
Water in Monster Hunter 3? The WORST.
Water in Sonic? Ugh.
Water in DK Country? THE WORST.
Water is only nice when it is an aesthetic element.
@Bold: Probably the worst part about the game.
Though I do think that in Super Mario World, underwater levels were fine.