I think the game has finally overstayed its welcome for me. At the last region, now, and I can barely work up the urge to continue. It's just so boring fighting the same monsters over, and over again. I've been doing every side-mission up to this point, and while I recognize that doing that is signing up for a certain level of tedium, it has kind of soured the challenge and excitement of the campaign (the fights are all I look forward to, since the story in this game is utter garbage anyway -- the cutscenes are just there for me to skip them).
I still enjoy going back and helping friends with coop. Still enjoy getting cool armor sets and fighting most of the bosses. But yeah, the levels aren't really getting better anymore (the end levels actually seem like a step back), and the encounters are well-tread ground. Having more missions and stuff will be good for any post-game grind that goes on, but yeah, I'm just sick of seeing the same enemies I guess.