These are a lot of suggestions, but some of them are minor, and others may already be in the works. However, I will say that I love this game so far, so these are just things that I think could make it even better.
1) Doors - I like the idea of having a small chance of it dulling your weapon, but another thing that could be cool is to have bashing a door give a chance to hurt yourself, lowering your HP by a little bit. That would certainly make you think twice about just brute-forcing your way through every door.
2) Minimap - Give an option to expand the minimap to the middle of the screen so that you can quickly look at exits / doors / chests you may have missed. While I like having the small minimap in the corner, I think it would be great if you could maybe click the Mini Map button twice and have it expand even larger (I guess at this point it's no longer a "mini" map though...!)
3) Spells - More! Cooler! (I might expand on this suggestion when I make sure I've seen all the spells in the game

).
4) Compare - Instead of showing the exact stats for the item you are comparing in parenthesis, it might be nice to show just the change (ie: +1 armor, -5 damage, etc)... preferably color coded for + and -.
When you pick up and item that was torn from your grasp -if it was previously in at quick slot -automatically put it back in quick slot so you do not have to find it in inventory to requip it. & show it the current quick slot of the active page so you know you have it.
Good idea, but it will be hard to implement. What I could do is to implement an Equip? Yes/No popup when you pick up an item of a type that you currently don't have equipped.
This was going to be another one of my suggestions. Maybe you could do a quick check to see if they can use an item AND if they don't have anything in that slot, and then ask if they want to equip it. Obviously you don't want a popup everytime you stand on an item, but I think the benefits outweigh the negatives if you do it for items that go in an empty slot.
Edit: More!
-Change the color of the targetting square to red (or something other than white) when you cannot target. The way it stands now, even if you can see the enemy on the screen, there may be some walls between you and him. When you are targetting them, it would make it much more intuitive if you could immediately see whether or not you can attack him, without first trying to attack and getting an error message.
-Modify the character sheet to show what items you can have equipped. For example, you could have little squares saying "head", "ring", "left hand", etc. This would quickly show you whether or not you have an item equipped in a slot or not. Furthermore, if you click on the box, it would be cool if the inventory could open up sorted by all the items that can fit in that slot. For example, if you click on the head slot, the inventory screen shows all of the items you currently have that can fit in the head slot.
-Remove the message summary after you sell items. It shows the items you sold, and how much money you got. So if you sell multiple items, you have to click through a message each time you sell an item. My issue with this is that it doesn't tell you anything new - when you sold those items, you knew how many you were selling, and how much you were selling them for. Why bother with the message summary at that point?