>>15757675
Borderlands 1 and 2: Remove the mechanic that gives you huge bonuses or penalties if you're overlevelled/underlevelled. This is a shitty mechanic for a Diablo-clone because it makes it almost impossible to play the game multiplayer unless the players keep their respective levels close to each other. Also trivializes the game if you become somewhat overlevelled which is an issue in BL1.
Borderlands 2 specific: Get rid of the ridiculous exponential scaling. It completely ruins the balance in late game and was only put in place to force the playtesters to replace their guns more often at early levels. Also makes the majority of the gear that drops at mid or high levels completely useless because it's a mere one level off.
Still won't fix the shitty writing, but that's a separate issue.