The story is mature and thematically complex, working on several levels and generally avoiding superficiality. The film is, unfortunately, not without its flaws. I'm guessing this might be due to the fact that the film progresses at a leisurely pace at best, and also that it simply attempts to do too much within its limited time frame. There are perhaps too many plot twists and turns and too many scenes that do little to nothing in terms of advancing the story. I think everyone should see this at least once, if only to realize the potential of anime to make really special meaningful film.
Wings is severely underrated, perhaps because it is considered too cerebral or sluggish.
However, you should see it anyway and make your own decisions about it.