I very much liked the musical The Last Five Years when I saw it in Toronto in September. It features Anna Kendrick and Jeremy Jordan in the story of a marriage that begins as the marriage is ending, leaps back to the beginning, and then follows the story both backwards (through the songs she sings) and forwards (through the ones he sings). They cross over in the middle at their wedding. It's a weird little structure, a little hard to explain, and while the trailer doesn't really articulate it perfectly, it's quite effective in communicating how good they both are in what's almost completely a two-person piece, how good the music is, and how much emotion is in this story.
It's hard to make an all-singing trailer and make it seem coherent, but they only have what they have to work with — the movie is basically all sung, and I watched what appeared to be a few surprised people get up and leave the screening early as they realized that this, people singing, was the whole thing.