Here is the plot outline courtesy of Wikipedia:
"The film concerns the imaginary adventures of a young boy named Max, who is angry after being sent to his room without supper. He then creates a forest inhabited by many large imaginary monsters, who crown him their ruler. He then befriends a large monster called Carol, who helps him understand the meaning of love."
Admittedly I was a bit skeptical when I first heard of the movie back in 2007, but the trailer actually looks good! I look forward to seeing more in the near future!