^to the comments above. The multiple playthroughs are....well for intense grinding and the type of people that are really into general looting and meta game stuff. If you just play the games to go through the, uh, lack of story, then there isn't much point to the rest. That's it, really.
I think that it's actually fine that a whole lot hasn't changed with this one. I think most fans want this to be not too far off what you expect. The main thing I still complain about is that the loot table didn't go back to BL1. ..so I want it to be more like the original game, haha. Further, I would have been rather angry if Goliaths didn't make an appearance here (the helmeted enemy that zeze was complaining about, which are quite literally, the most endearing enemies to mess around with in the game--there's a reason we love them so much). For me personally, I really just don't like FPS games in general--yet this is one of my favorite game franchises ever. ...which means this is the only FPS I really play. So if you look at time spent in game types, Borderlands time played = all FPS time for me, so I scratch that itch here...which helps that these games are specifically designed for replayability more than most others.
...but all that being said, It does feel like too much of the same thing, eventually. I still haven't finished the main campaign, it is preposterously long. I'm in the final map (presumably), I'm already at level 41, so wondering why it is balanced the way it is for a max level 50 character? I guess the side quests are much like BL1, where they massively overlevel you early on...but this one has proper enemy scaling, so I certainly don't feel overpowered at all. Anyway, I don't really see myself doing many playthroughs, especially through multiple characters. That is sort of a no-brainer for me in the past, but I feel like the first playthrough is just way too damn tedious for it. Granted, 2nd playthrough is usually 2x faster if not more, but I just don't get the same sense of fun with this one that I did before. It all depends though on spending time with other characters and if I like those playstyles enough to continue on. ...and the quality of the eventual DLC, and how they handle scaling with the new level caps.
It sounds like they are certainly not going to release new characters at any time, which is a huge bummer, but that also removes some of the "burden" from thinking that your disease will force you to churn through that many playthroughs.