First thief past level 20 or so.. as it turns out, uncaballed Elf thieves take a huge amount of time and effort to not get utterly steamrolled.
Doesn't help that literally every one of my enemies in my play-times could see hidden, and easily take me down one-on-one. Did have a couple decent PKs in there, but for the most part I was happy just putting up a decent fight then surviving.
Good experience, enemies were classy. Friends were.. friendly. Good experience, I just couldn't do it anymore.