So much fun. Nostalgia is amazing and they follow the movie fairly closely. Doc Brown completely steals the show.
If I'm being fair, most of the music is mediocre which is the only downside. But it makes up for it in fun, humor, and nostalgia. And the music that matters is amazing: Power of Love, Back in Time, Johnny B Goode, and Alan Silvestri's score.
If you're a fan of Broadway shows you should go see it. If you're a fan of BTTF you HAVE to see it. Can't recommend highly enough.