Currently designing my own "tabletop" system as I have a number of issues with standard d20.
My thoughts on armor/weapons:
"+" and "-" were once awesome and made upgrades easy to identify. However, they have been supplanted by thematic upgrades. Examples: build quality, material, magic properties, item history, and upkeep status. Upgrades are not as easy to identify, but us min-maxers love a challenge.
I strongly believe that a player should be able to end the game with the same weapon/armor that they started with. Crazy? My reasoning is that we often find ourselves looking for that next legendary item such as a certain dark elf ranger's scimitars, but what makes these weapons special from any other weapon? True magical enhancement - or more likely - the user imbues something into the item. So I like to make means for players to create the legendary items for the next generation.
No limitations to armor/weapons via class. All items have pros/cons and are easier to use given certain skill sets or abilities. A strong rogue may wear plate armor and still maintain the "class" ability to sneak, but it sure will be difficult as plate makes a hell of a lot of noise unless you have been trained for years specifically to sneak in plate because you've been assigned a position in the royal guard. Phew. Point: allow player choice -> enforce consequences.
Real armor and weapons aren't drastically different in terms of protection and damage, but rather provide a variety of secondary modifiers. So rather than look at armor as purely a range of ACs, I like to tighten the range, leave true defense and offense to player ability and choice (e.g. stances.) I then put secondary effects, like plate making noise, chain protecting from arrows, elven mail gives diplomacy bonuses when talking to elves (unless you're an orc, then it'd likely be a negative as they assume you got it through undesirable means), cloth armor catching on fire easily, master work weapons have a higher critical chance because they hit like a ton of bricks due to solid construction, master work armor can withstand more as there are less gaps, armor made by people who live in cold places likely protects from the cold, etc.
Those are the basic principles, from there I generate arrays of keywords and nouns that sound like something I would want to loot.