What's your favorite roguelike feature?

Just tell me - what's your favorite roguelike game features - no matter whether it's in ADOM, Angband, Nethack or whatever (and please tell me the game, too). Just thinking about which cool things should go into JADE first in the time to come.

Thanks!

The completeness of JADE

Since I continue to be surprised a little about some questions like "Why is there no gold in the game?", "Why did you miss this bug or that bug?", "Why is there so little content?" I just wanted to remind folks of what I wrote a couple of weeks ago here and here.