The simplest thing to say from a consumer guide perspective is that if you love Bruce, you'll like this movie. If you love his latest album, you'll love this movie. If you don't have an opinion about Bruce Springsteen, I'm not sure what you'll think, but it will give you insight into a 70-year-old rocker who still has a lot to say.
There are two things to address here. One is the music. At its core, Western Stars is a concert movie, where Bruce and a large band play the songs from the Western Stars album. He has a huge string section, and they kick ass ... their unison playing gives the songs something of a Phil Spector feel. As is often the case with Bruce, the songs benefit from being played live. Favorite songs are even better, songs I didn't much care for are better than I thought. If you're looking for familiar faces, you'll find Patti and Soozie and Charles and Lisa. The music sounds great played in Bruce's old barn.
The other thing is the movie-as-movie. There is no escaping the fact that the songs, and their performance, are what matters. But it's a gorgeous movie, from the way the inside of the barn is lit to the wide-open spaces of Joshua Tree. The brief commentary that accompanies the songs is just enough to expand our appreciation. It's hard to find anything to fault in Western Stars as a movie.
I don't know if a newcomer to Bruce would be convinced by this film. Emotionally, the songs represent a culmination of his life's work, but the music is different from his usual, and I don't suppose you should start here. But for long-time fans, the movie adds greatly to the album. The intimacy is lovely and rewarding.