It makes you think beyond the story it tells. At one obvious level we have a dramatisation of the damage done by pointless social condemnation of love. But that 'message' could have been conveyed by a much simpler film. This one is more like 'Crouching Tiger Hidden Dragon' because it dramatises the needs of conflicting sympathetic characters, and suggests rather than answers the difficult feelings we struggle with.
For instance, what is the relationship between the early promise of love and a long term relationship? What do you lose if you can't settle down with the person you love? What do you lose if you can?
Most importantly, I think the film explored what love really is, apart from the social conventions of how we ought to show love, how we ought to behave. Real love is something that smashes through life, and I don't think anyone has found a good way of coping with it that doesn't compromise it.