I really like the clever use of minimalistic graphics and sound.. minimal indeed, but contributes immensly to the atmosphere of the game. Infra Arcana has much more immersiveness than several mainstream million dollar games.
Very nice classes and skills system as well; each class requires a different approach to the game and makes it a new overall experience. (However for the sake of plot it's a bit weird to think about a ghoul getting phobias and finding psychological comfort by holding a flare and things like that - also why the heck was a ghoul venturing there)
I also like that the game is now quite hard. There's almost no zero-challenge enemy.. minimal backtracking, and the new xp system is clever, fun, and ensures there's no grinding. Reasonably good also for how much the mechanics are made clear to the player (damage input per weapon, chance to hit modifier.. and also chance to hit per single enemy, however it's a bit tedious to check as one needs to press a few keys).
As Legends said, the game rewards exploration rather than mindless killing of enemies. So many times however I found the stairs early but died in the process of exploring the dungeon a bit more before descending. Possibly the game rewards equally exploration and getting the hell out of there as soon as the stairs are found..!
Absolutely excellent game, and a pure roguelike.