If you like music, you'll like this film because it is a story about love for music, there's also time for other love, yes, but the main purpose of the film is showing the love people have for music and how this thing can help you overcome things and change your live. I've heard some critics say that this movie "has a soundtrack for every love story" and "a movie for those who live life as if it was a playlist" and I also would define it like this. If you don't like music, or it is not one of your most loved interests, this film makes you appreciate it. The places where the music is made captivate the viewer and the songs make you spend some good time watching the movie.
As for the story itself, the base, I wouldn't define it as groundbreaking story because if it wasn't for the music component, it could have been entertaining - because it is not a film about how a music star is born- but it wouldn't have been that good. As said, Keira Knightley's character, Gretta, does not want to be a star, his ex-boyfriend has just started being acclaimed and at the same time broken her heart. So this is about second chances, and Mark Ruffalo and his great perfomance of his character, Dan, also needs one. Both, Gretta and Dan are going to tell a story which can be predictable but that is always defined by music and how music is present in all kinds of relationships.
I've also heard that this film makes you come out of the film with good vibes, and it does, because it's a simple story with a simple broken love relationship and a bad father-daugther relationship. But less is more, and that simplicity, along with sensibility, becomes one of the most remarkable things of the film. Another remarkable thing is that it is a romantic story, but it isn't cheesy, it is just a confluence of two people that have problems and solve them together because one thing has joined them, music.
Probably, this is that kind of movies where you say at the end that it was better than you expected.