Definitely agree with Halo being mentioned several times. Personally I found Halo 4's soundtrack to be somewhat lackluster by comparison. Just didn't have the same oomph to it.
I'll mention Dragon's Dogma (vastly underrated game anyway). What I loved about its music is how it contributed to making me want to spend time in that world. Even grindy quests weren't so bad anymore since I enjoyed just being in the world. The music helped a lot there.