Yai, I wouldn't say it's boring, it's a weird thing for me though, as typically I don't find games dull even if I don't enjoy them. And I wouldn't say I don't enjoy Borderlands 2, I had a good amount of fun with it during the first 30 hours or so, but after that it's just been declining interest whenever I happen to relaunch it again to play with friends.
I'm the type of gamer a game usually doesn't feel dull to me if there's some element in the game that I find interesting or fun. I can play an admittedly pretty mediocre horror game for example if there's some element about it that I like, such as the atmosphere or the look of it, or if it has good music or something. Which is why my reaction to BL2 I find a bit of an oddity. Hell, I don't even find bad games dull if there's something so bad about them that it's entertaining in its own way.