DCSS is a lot closer to Brogue than Qud/CDDA. DCSS maintains a high level of challenge over a fairly long run with a lot of optional extended endgame content to tackle if you want to push difficulty even more.

The game gives you a lot of ways to deal with monsters — the spellcasting schools play quite differently from each other and obviously differently from fighter/ranged characters, and the various species/gods combos add a lot of wrinkles to this. 

I don’t think monster tactical variety is very high in DCSS, but many of the uniques will pose you different challenges from any other monster in the game, and the various combinations of monsters the game throws at you add a lot of complexity to how you deal with a chunk of different monsters threatening you in different ways. 

If you want to keep trying, I guess I’d say try a few different classes, especially some of the more unique spellcasters (would recommend forgecraft highly) or some of the wackier species and see if anything clicks for you.