I have been working on one of my big projects lately (I even got a 3d engine), and have been wondering how to create an elegant inventory system. I really like the way Ultima Underworld and System Shock games allowed you to directly drag objects from the envirorment into your inventory, or vice versa, and I would like to try something similar, however at the same time I also want a small HUD, where most of the screen is for viewing the world. A limited HUD, and an easy drag and drop inventory system seem to only work together if I have a popup inventory, of which I am not too keen on. Oh well, any ideas? What kind of RPG inventory systems do you like?

I think you've pretty much got to go for the popup inventory - but this can be minimal - on clicking and dragging an item to the bottom of the screen you can pop up a small target for drag-drops. Shouldn't be too intrusive.

I like hold-right-button context menus, and single right click to activate default as a mechanism, coupled with pointer / reticle changes to indicate the default action (attack, examine etc).

I also like being able to decouple the pointer from the reticle in first person views - having to precisely aim at a button you're standing next to seems a little silly to me. If I can hold a key down to move the 'pointer' away from the centre of the screen I'm happy.

This is a general interface thing though, and not explicitly tied to inventory as such. I do like paperdoll behaviour for equipping / unequipping from what I'm carrying though - I think it's intuitive. If you allow a pull-back to third person camera feature, you can treat the player's avatar as the paperdoll, which I think is a neat immersive feature. You're still going to need a popup window system of some sort to represent containers though.

I was thinking of having some quickslots on the bottomleft and bottomright corners (where you keep track of equipped armor, weapons and containers), and a larger pop-up in the bottom middle when you use a container. You can decouple the cursor in order to drag items back and forth, aim, and use items. I think it should workout nicely.

I also have been thinking if every item in your inventory takes up only one square, or if bigger items take up more space (such as weapons and armor).

The system planned for Bloodspear has two stats for items - weight and bulk.

Bulk determines ths size of things, and relies on agility and dexterity. More agile people can carry larger items. Bulk is also the main limiter on what can go into a container. More dextrous people can carry larger items one handed, before needing two free hands to carry them, and more smaller items.

Weight determines, uh, the weight. Strength is used to determine carry weight. Occasionally a container may have a maximum weight limit, but this is unusual.

I don't particularly like playing inventory tetris, and I think balancing these two stats should give players enough problems.