Weapon crafting. Parts are broken down or obtained directly as loot and are sorted by brand, i.e. dahl, tediore, etc. obviously rarer weapons provide rarer parts and allow more powerful upgrades. Furthermore, even common weapons have a chance to supply rare “core parts” which would be non-brand-specific parts that can be applied to any gun to improve it’s core stats like damage, accuracy, etc. These bonuses would be very small, but over time with many core parts put in the same weapon, could drastically improve it’s performance. (a similar effect to badass tokens, but amplified and only applying to a single weapon rather than all characters across and account.) Rarer weapons would give higher chance to break down into core parts, as well as providing better parts in general. Crafting and breaking down weapons into parts can only be done at a workbench which gives more realism and makes inventory management more relevant. This gives even the cruddy loot drops a purpose as they could potentially break down into valuable core parts, but also still forces you to manage your drops due to inventory. This would make it important to find and keep track of workbench locations.
Taking the feel-good needles to the next level, there would be a drug crafting system as well. You could make and keep needles in your inventory which had various effects. Stat boosts, cool-down reductions, health recovery, etc over a short time. Get drugged up before a big fight to add another layer of strategy to the chaos. enemies, particularly non-human ones, could drop ingredients (or their body parts to be more specific) which could be used to make different drugs.
For both weapon crafting and drug crafting, certain levels may be needed to make certain items, or possibly skills spcifically for crafting. Alternatively, all things can be crafted in general at any level, but the effects of crafted materials are stronger the higher your character level.
Character skills would be more diverse in that each character could have more than 1 action skill-- perhaps 3 (1 for each skill tree) with many supporting skills still. Each action skill could have separate cool-down timers or activation requirements so that you could use more than one at one time creating devastating effects.
The story would take the concept of “infinite vaults” to the next level! Your journey takes you through a planet rather quickly where you face off against a baby vault. It’s guardian is in its infantile stage, and not nearly as powerful as a final boss would be. From there you learn of the vaults scattered around many planets, and conveniently enough have a tinker friend who can build you a spaceship. I know right, who’d of thunk? You can probably upgrade the shaz out of this thing too, and use it to get around to the next place. (I’ll leave that crap to you). Anyway, the game ends when you reach the final planet in a series of mayb3 4-8 different planets. climatic battle, awesome loot, yada yada end of game, right?
Wrong. I give you, the post-game, longevity boosting, replay-value creating, key drawing point of the game-- RAIDS. Looking at a lot of successful long running mmo type games (even ones I can’t stand), I realized that most of them share the same basic end-game concept. Once you’ve done everything else, you enter randomly generated, super rewarding dungeons, or instanced combat scenarios which you do over and over again. Usually these are not even that intersting and yet people play these same mmos for like 10+ years. So, you have whole planets to work with because that is the concept of the game anyway. You travel to a randomly generated planet which will have random weather, terrain, creatures, etc. Each planet would be relatively small (or at least limited in how much you can explore), that way one raid wouldn’t take 10 hours, but would still offer enough freedom and exploration to feel satisfying and rewarding. The end-goal to the raid, is to find and conquer the vault and obtain the loot therein. planets that you found particularly fun could be added to your GPS to return to, and it could regenerate that same planet. You can invite up to x amount of other players, set rules for joining such as level requirements, pvp allowed or disallowed, etc.
This is what I want to see in Borderlands 3.