I never had a problem with anything on my old sneak archer character, but my new one is a melee, so mages frying me while running away from my great sword pisses me off now.
Ran circles round one of them last night....Those huge centurion robots in the Dwemer ruins can be a pain too.
The very first quest I did was in the Shimmermist Cave. Those Falmer and Chaurus were killing me over and over. I haven't screamed at a game like I did that day since trying to beat the Arishok in Dragon Age 2. I'm pretty sure 50% of the obscenities I screamed were made up gibberish.
Luckily they are much easier now.