I have like over 600 hrs in borderlands 2, and that's only counting the PC version. I just find the game to have insanely great replay value. I've gotten to max level with 5 out of the 6 characters so I still have one other character I have barely even started. The game, with all the dlc, has a ton of content so I never really get bored of doing the same thing too often because there's so much to choose from. The tons of different weapons, items, and different character playstyle and builds keep the gameplay pretty fresh. Also a lot of farming for gear, which isn't fun and I won't defend that part of the game. At this point I've basically farmed everything at least once so I just hack in or edit items if the farm would be too boring.