Inventories generally are boring.
Best is something like oldschool FPSes (Half Life 2, Serious Sam...): you have what you have and have a key-binding to pull it out when you want. TF2 has had the most impactful itemsets of any game I have played. Some items completely change how a character plays (like Charge'n Targe making a defensive, lane-closing Demoman into an offensive, charging frontliner).
In terms of RPGs, some good elements from games included
1. 2 Weapon loadouts to switch between. Diablo, The Sith Lords, etc. have this. Removes some of the tedium of swapping loadouts. Would be better if you could save multiple loadouts as templates, see them with their name on top in the character-viewer as a tab, and switch between them as desired. Like TF2's ABCD preloads.
2. Filters and columns. Morrowind's grid with keywords you could select and auto-organize options was much, much better than Skyrim's graphic's art's major object art gallery. It's more important to convey information than to showoff the model of an art asset.
3. Mod focus. Spiders series of games tend to have fewer main item pieces but more modular sub-parts per item which you as the player can customize. I like this approach as it emphasizes the player as a co-author in the functionality of an item. Want a certain build? You can probably make it. It's lame in games where you have these fixed, pre-assigned designs which may not combine the tradeoffs you want to optimize.
4. Mod impact. Mass Effect did well with letting the player reduce cooldown, add poison affects, stabilize, etc. weapons so you could make them perform how you wanted. ME did poorly by not stacking identical items in the original game, making trading agony.
5. Auto-equip patterns. Dragon Quest and other jrpgs let you set, "offense, defense, mp" and other specialties so when you get a new, better item the character immediately equips it according to their stat-schema. This eliminates the tedium of having to manually open the equipment menu every time you get something, equip it, and leave. It helps with gameflow.
Way too many rpgs have this grind-tastic focus on randomly-generated, marginally-different weapons. It turns the whole game into a Skinner Box. Many of the entries in the hack'n slash genre, mmos, borderlands, fallout 4, etc. have adopted this approach where you don't engage in combat as a fun end-unto-itself but as a means to roll the slot-machine of a loot drop and see your stat numbers go up...even though you don't need higher stats to win combat so they are meaningless. Inevitably your inventory maxes out and the gameplay becomes a cyclical chore of re-organizing your inventory, selling off items, breaking them down to components, crafting, trying to max-out every stat, etc. You spend more time faffing about with items than you do fighting or talking. Inventory/item management de facto becomes the main gameplay loop.
So please no weight limit or grid space limit.
