I've been playing your game over demo day and I'm really enjoying it. I'm a fan of Diablo 1 and 2 and so a lot of the controls and UI was intuitive for me. I knew the map would help navigate the different floors, but perhaps a newer player to the genre would struggle to find the doors in the corner of a dark room.
Even though it appears to be a Diablo clone I did like your unique touches such as the cards representing the allies and the fact that allies join you on the quest (furthermore I saw the pet dog, and when we was all fighting the minions I was getting Gauntlet multiplayer vibes, very nice). The loading screens have a hint of the Skyrim loading screens which I like too. Seeing I could equip items onto my allies was an exciting feature. I'm not sure yet if the allies will be temporary or permanent but it will be nice to customise the whole team.
An area which could be improved on is the NPC textbox UI. I think it just needs to match the rest of the UI in your game and I think it will look fine.
I did encounter what may be a small bug. I did get Alberich killed in the mines. When warping to the town I saw and recruited Blathmac and this recruiting action actually revived Alberich.
A 2nd softlock bug I found was when buying a potion. To replicate;
1. Click a potion from the priestess. (So that the potion is on the cursor).
2. Press Escape
3. I wasn't able to move or re-click the priestess (save and quit then reload does fix the issue though).
I like what you are creating. I ran full-screen on windows I didn't notice any performance issues.