I was up to Mayhem 1 easily with some cheap runs of Mayhem 10 (didn't play when 11 came out) and had a good enough time with it. The game itself, for story, absolutely sucks. DLC 1 was probably the best part about it all told and that was because Jack was back. The gameplay was stellar, and a logical progression from how good 2 was, but it's not something I would tell you go out and buy for full price.
And don't get me started on the second season pass, good God. That was the worst thing Gearbox could've done to themselves.