Well, the music of Pirates of the Caribbean movies comes to mind. That's some of the most uninteresting and derivative stuff I've ever heard, and yet I can't help but like it (while I think the first two scores were awful, I was positively surprised by the third score despite its similarity to the two previous scores). And as we're speaking of derivative music, (not-so-)honorable mentions should go to the soundtracks of both Transformers and 300, both of which are big ripoffs and yet I enjoyed them for what they were worth. These are definitely guilty pleasures for me.