The story is non-linear, with some kid I don't know or care about trying to find out where trees went. Then we get an incredibly long backstory with a different through-character. I'm not sure why they didn't just start with that story and then follow his character forward. Perhaps that's the structure in the book? In either case, neither character is really strong or interesting enough to justify a film. The Lorax character is, especially with the strong casting of Danny DeVito, but that's not where the story is. (Also well cast is Betty White, whose presence is wasted.)
It's weird watching such interesting animation only to have it on such a mundane story. And of course the film is a ecological cautionary tale, so if it had been told well, it could have been a much more important movie. Too bad.