Not the most interesting answer, but I've yet to see another roguelike with such a great interaction between powers, weapons, items and the world.
If you find a bomb it can damage enemies or yourself, or blow a hole in a wall revealing a secret room, or blow a stone up possibly making it cover a hole, or blow up a door, or blow up a machine, or blow up background stuff, or use the explosion to push items around.
You can have different types of bombs, you can end up firing bombs yourself, you can find bombs, you can buy bombs...
So many things in the game can interact with other stuff. The way your powers can interact to create different ways of attacking is impressive enough, but the world you move around in is also affected and can affect you.
The game is way too long and luckbased if you're going for the final endings/achievements. But you can get many, many hours out of it before it gets too dull.