The main character here, Roddy, a spoiled pet rodent (I'm not sure if he's supposed to be a rat or a mouse), is voiced by Hugh Jackman (Wolverine from the X-Men movies), who seems to be in every other film released this year (according to IMDB, he's in seven) ... I guess he's padding that retirement account while he's a hot commodity! Actually, there must have been some fun times in the recording studio, as Ian McKellan (X-Men's Magneto) voices the villainous "The Toad", and I'm sure there are some amusing out-takes where these two over-laid the two movies' roles. Among other "names" doing voices here are Kate Winslet as Rita, and Jean Reno as "Le Frog" (with his squad of French ninja and mime frogs), as well as Andy Serkis (Lord of the Ring's Gollum) and Bill Nighy (Pirates of the Caribbean's Davy Jones).
Roddy, a spoiled pet rodent, finds himself (through some mis-adventured) flushed down into the sewers, where he discovers a whole new world. At first he's just attempting to get back home, but when he realizes the extent of The Toad's dastardly schemes, returns to save the day, get the girl, etc. The plot moves along with enough twists and surprises to keep the adults happy, while not being too confusing for the kids (I did have to explain why the French frogs all snapped into a surrendering pose at one point, though). The film is filled with in-jokes and references to other movies, though ... some that I caught while watching (the books on the shelf by Roddy's cage), most of which I read on the IMDB boards.
While The Girls seemed to like this fine, I was surprised that I enjoyed it more than The Wife did ... it reminded me a lot of Valiant (the animated "wartime pigeon" movie from last year) in its tone and pacing, and I seem to recall I liked that better as well. While not a "must see" for adults, this was certainly an amusing film, and not a bad option if you're up for an animated feature starring assorted rodents, evil amphibians, and (did I neglect to mention?) singing slugs!