Although not terribly orginal in concept, the movie is enlivened by funny characters (the bucktoothed Ardman designs look very natural as rats--), visual gags, and humorous incident, plus concepts such as the singing slugs that provide a sort of ironic Greek chorus on the action. We are going to have to go see it again just to watch for the visual jokes. (For example, searching through his owner's dolls closet for something to wear, Roddy passes over "Wallace's" shirt and sweater-vest, before settling on an Elvis-style spangled shirt.)
The movie has comic-thriller action, but no one is killed, and it's a very NICE sort of sewer to be in, over all. Amazingly, there is only one "excrement" joke, and that is a throw-away sight gag referring to an infamous bit from another movie. Good for almost all ages, although some sequences such as the high-speed boat, may be intense for younger children.
Although Jackman, Winslet, McKellen, and Reno "act" their parts perfectly well, I can't say that the production was necessarily enhanced by any of these stars. I am reminded of a statement made some years ago by veteran voice actor June Havoc (the voice of "Rocky the Flying Squirrel")lamenting that the trend to use "star" voices in animations (fueled by "Shrek" and others) was taking opportunity away from people who had built careers in voice acting. Indeed, there's really not much about any of these roles that a hundred actors couldn't have done as well.