I find that, while I've tried a few rougelikes, far and away the most time I've spent playing is Diablo II and DoomRL. So this reply is mostly about them.
Items: In my preferred rougelikes, items are relatively simple. Often, they can be modified (slotted items, upgrade packs), but they do little other than their intended function.
NPC Behavior: I like 'em simple. I don't much care for exploitable behavior, but I do like the old-school black-and-white morality. I'm not here to understand what motivates my NPCs, I'm here to separate them from their tasty, tasty EPs and swag.
Interface: I like a simple interface. I prefer games which are designed to enable ease of control, rather than depth of control. I'm not going to quaff a wand, nor fire a helmet. I've never enjoyed fighting with the computer to try and word a simple action completely. Any one who's played the text adventure games of the 80s knows what I mean.
I'm totally happy with "equip," "use," "alternate use," "combine," etc.
Equipment Upgrade Path: I'm pretty flexible on this one. As long as it's easy to tell if the swag I find is better than what I've got, I'm fairly good. Oh, and I should be improving fairly often. This can be leveling, new gear, or whatever, but there should be a definite feeling of progression. Infrequently enough to be satisfying, but frequently enough to be fun.
Power Curve: Again, it can be steep or shallow. As long as the game is consistently challenging, without being overpowering, I'm happy. Of course, without some power progression the game gets boring, but I don't care whether I get large or small power boosts when I level (or whatever).
