There have been some pretty mediocre movies with pretty good soundtracks IMHO. I don't tend to care for the weepy stuff, or anything that's trying too hard to be artsy. A few of my old favorites:

The Not Another Teen Movie soundtrack. Cheesy 80's music covered in an eclectic way by 90's-ish artists. Orgy does a superb techno Blue Monday, Marilyn Manson does a dark Tainted Love, and System of a Down works over The Metro. Pretty unique, interesting soundtrack IMHO.

The soundtrack from the first Mortal Kombat movie (Don't go watch the movie... well, okay, go watch Reptile's fight scene and skip the rest of it ). Energetic.

Reservoir Dogs soundtrack. Duh? Gold right through, especially the KBILLY song intros from that deadpan comic dude.