I was surprised with how much I enjoyed this movie. The plot basically consists of various members of the Rugrats meeting various members of the Thornberries, and thus it feels a little scattered in places. Still, it hangs together on the strength of the humour which did have me laughing out loud in places.
Bruce Willis as the voice of Spike was a definite scene-stealer. He manages to combine a wise-cracking brashness with just enough stupidity so that you believe that Spike is still a dog and would still quite happily drink from the toilet given the opportunity. And who knew old Bruce could sing? His duet with the clouded leopard, Siri, is easily one of the most memorable songs in the movie.
Also the toilet-bowl humour that I felt ruined "Rugrats in Paris" has been greatly reduced in this film which I was very glad for. Lil even spends part of the movie trying to convince Phil they need to stop eating bugs.
If you enjoyed the Rugrats TV series or the Wild Thornberries TV series--although they appear in the movie to a lesser degree--you'll probably have a good time with this movie.