Doombringer is by far my favourite class, since I've always been fond of melee/mobility/pyromaniac builds. Pretty much made Arcane Blades obsolete for me. I would say, however, that Doombringer is admittedly a little overpowered. Demonologists on the other hand are in dire need of some buffs. The whole demon lore you get to read is very interesting, although there are lots of parallels to Orc lore. The new artefact items have some nice effects, too!
I donated earlier, donated again to buy the expansion, then donated again because I liked it so much.
But that's only because the way TOME takes out some of the micro-managing and RNG-dependence of classical roguelikes and replaces it with tactical combat and customisation just really clicks with me. Roguelike purists may not like it, and even beyond that there's a lot of questionable design choices in TOME...but still, I recommend it to anyone. It's free. And the donator-only content is actually neither overpriced nor bad.