I dont mind the extra difficulty or if they gave some mobs different effects to change things up, but the UVHM increase in difficulty was poorly thought out and it is a lazy way to make the game harder. Rather than think things out or make interesting changes, they turned enemies into ridiculous bullet sponges that pretty much force you to use slag. Some enemies were already boring bullet sponges that required a lot of bullets and increasing the hp only made things worse. I enjoy difficult games, but games that multiple the hp on mobs in order to make things more difficult fail in that department. Extra hp just means more tedious rather than more difficult. The only system that is worse in trying to make a game more difficult is infinite spawning mobs until you pass imaginary lines.
Once you get use to the new system, the game isnt much harder just more boring and tedious as you apply slag then switch to another weapon to unload endless shots. You really dont need a lot of new strategies, just the ability to move from cover to cover until you finally dwindle down the mobs giant hp pool. Slag was a poorly thought out idea that shouldnt have made it into the final game especially since co-op is a large part of the game. Before now if you had someone on slag duty in co-op, it made killing things much easier, but since most groups used it, they had to tune the game around it. Instead of it being a luxury, it was turned into a necessity. They werent happy with everyone using fire elemental guns in BL1 bc the effect was the most powerful and now they forced everyone to use slag in BL2 at the highest difficultly. Once you get the better gear at lvl 60, things arent as bad, but even then killing/farming bosses and areas is more work than fun now.