Werewolves. Doesn't really affect me, but I just like seeing wolfaboos anguish over not being able to reenact Twilight in-game.

Most other creatures I can tolerate, but I really, really wish there was mounted combat. In Oblivion, riding through the wilderness basically consisted of:
>Riding around.
>hear le battle music.
>Wolf attacks horse.
>Get down from horse with an incredibly leisurely animation.
>Kill wolf in one hit, sending it flying thirty feet backwards.
>Recharge weapon with wolf's soul.
>Heal horse.
>Mount horse.
>Repeat step one.

Then just don't swim. My mage doesn't like getting his robes wet, so he uses water walking anyway. And I don't want to start hating Dreugh.

Bonewalkers, I hate them with a burning passion.
I consumed a ridiculous amount of potion because of their attribute svcking.