Sexism and Abuse
My major problem with this movie was the fact that Ted was doing everything to attract Audrey. He didn't care about trees or the environment or anything, and this was even called out during the film in a quite sexist remark from the Once-ler's side: "If a guy does something stupid one time, it's because he's a guy. If he does the same stupid thing twice, it's because of a girl." Then, at the end, it seems like Ted suddenly grows a conscious and decides to plant the seed for the greater good of the town.
That's not the only inexplicable 180 that characters tend to do. The relationship between the Lorax and Once-ler also seems a bit contrived, with Lorax trying to get rid of and then saving Once-ler and...that kind of ends their character development. Where the relationship between Once-ler and his family could be explored, it is merely explained away and falls flat. This could have been a series of empowering scenes detailing how controlling and "poisonous" relationships, even within families, are not healthy, but instead it's overlooked.
So: Sexism, ignoring abusive families, not developing potentially great characters. I'm sure there is a message about polluting and conservation in there, but it seems random and tacked-on rather than the main focus. Read the book instead.