Celestials have the most annoying starting area, in my opinion, it's not just about the classes being weak early. I mean, the Maggot is probably harder, but at least that one's optional. I've had moderate success with Anorithils, but it's tough to get past the early stages, and their weird casting resource mechanics take some getting used to.
Inspired by this thread I've gone back to ToME a bit myself. I was trying out Cultist of Entropy, but it does not quite click with me. I think it's the complex juggling of status effects that turn me off a bit - I like to play ToME in a more casual way, where I don't have to think that much during gameplay, but with Cultist I have to keep track of my entropy levels, as well as the various effects that trigger upon x numbers of casting or x numbers of applied debuffs, and it impairs my enjoyment a bit.
I think I'll start out a Doombringer instead - I usually find that a nice antidote when I come off playing one of more complex classes. Sometimes you just want to stride into melee in heavy armor and set fire to everyone.