I took my kids to see this when it came out in the theaters and we all thoroughly enjoyed it. Unfortunately, it didn't do well up against such competition as Santa Clause 3, and the critics panned it as a painful mismatch between DreamWorks's CGI-based approach and Aardman's trademark claymation. It also proved to be the movie that broke up the pairing between these two studios.
While I could see the point, to some extent, of critics who felt the movie was too American for Aardman and too English for DreamWorks, and never the twain should meet, I found the fusion of off-kilter British humor with frenetic American action to be quite entertaining. I laughed out loud more than once in the theater, and my kids enjoyed it as much as I did. It's rare these days to find a movie the whole family can enjoy without the parents being occasionally uncomfortable with off-color humor aimed more at adults. Flushed Away was definitely a family movie, and we all liked it, critics be damned. And the singing slugs? Hysterical.