1. The equipment screen is a little backwards. Whenever you try to select a slot that's already filled, it always seeks to unequip that equipment. I suggest that, if there are alternatives to put in the slot, there should be a menu (like using something) that gives you the option to equip any of those alternatives or to drop the equipped piece. Since you can already do the same thing from the inventory screen, it makes a lot of sense for it to go both ways.
2. Some of the coloring makes it really hard to notice what you're missing, particularly when you see so many different objects using that dark red color. Maybe switch up some of it? Barons and large med-packs could be pink, for example, and lava's red color should be bright red instead. All the bloodied tiles and bloodstone really obscure things.
3. It'd be nice if your stats screen factored in everything. Berserk modifications, for instance, have no obvious effect on the stats screen, but it's obvious that there's a speed bonus. (If nothing else, a little indicator with something like "Berserk State: +##% speed" would be awesome.) Also, current/total monster kill would make those min kill badges a lot easier to determine if you're anywhere near having a shot at completion.
4. Currently there's no choosing mechanic for multiple copies of quickkeyed weapons. If I want to select my power-modded pistol instead of my tech-modded pistol, the game only picks the top one from the inventory screen. Even more infuriating is trying to use another weapon with them. Suppose I have a combat shotgun in the weapon slot and a pistol in the prepped, and I quickkey for my other pistol: the game just swaps my weapons and forgets about the other pistol. (This is remedied simply by not using the quickkey functions, I understand, but to have them there at all should imply they're functional whenever you need them to be.)
5. Whenever a homing phase device isn't going to work correctly, I suggest that there should be some kind of message to indicate thus (basically just Hellgate and Phobos Arena/HF, could apply to other stuff as necessary). "Cannot detect available exit. Phase anyway?" Also, do multiple exits (ala special/normal and Mortuary) provide a random exit, or is there an arbitrary given?
6. The 'wait' function always spends one second (10 turns), regardless of anything going on. I suggest that it contain an exception for approaching enemies: if the enemy comes into view during any turn of 'waiting', then it should end prematurely. Sometimes I wait and an Arachnatron still manages to approach AND fire a volley...that always seemed off to me.