Philip Glass wasn’t just trailer music for Watchmen. The music actually is in the movie! And it is interesting because had Elfman, and not Tyler Bates, scored Watchmen that’s what I’d imagine the music to sound like. Elfman has said on numerous occasions that every now and then Glass pops up in his work. Since Zack Snyder, the director, is obviously a fan I’d imagine he’d be fine with Glass-esque music.