Thief: Black Powder is the stupidest name and concept for an attack ever. I really wish it was ineffective so that I could never use it. Pistol Whip is almost as bad; ditto.
Mesmer: I won't begrudge the illusions poofing, but it'd be nice if the phantasm that takes half my damage would stick around between *enemies* since I usually bring it out for tough fights. Sigh.
Guardian: Wow, it's been a while since I played this one. Maybe I just don't like Charr.
Ranger: The raven is the coolest looking pet I've found so far. Useless, but cool-looking. Uselessness is mitigated by pets' general fragility and the difficulty of hitting function keys during combat.