I see a lot of people say they need a challenge or the difficulty needs be increased but can never really elaborate on how to do this. Right now “difficulty” seems to be to just up HP of enemies and make them deal more damage, but even if all enemies one shot you and needed a whole ammo pool to kill the game would not be difficult. You just need to sit behind the right wall or rock and have patience. Even Malawian Takedown M4 is pretty easy if you just take your time and go slow.
Real difficulty IMO would be to improve AI, flanking, swap weapons, sneaky suicide bombers, snipers that don’t run up and melee you, but all that is way easier said then done and I just can’t see it being implemented, therefore borderlands will never truly be difficult.
Credit where credit is due though the bosses in this game do a pretty good job of it, having dodge-able high damage moves if you pay attention to the ground and their actions. Only downside is this is Borderlands, so your most likely using builds that melt bosses in 1-5 seconds and never really get to experience their whole move set more then your first play through.