It's good, but not good enough to be Aardman.
I enjoyed Flushed Away from start to finish, don't get me wrong. There were lots of great characters, madcap adventures, a wonderful world, hilarious spoofy jokes, and whatnot. And the slugs were wonderful. Worth rewatching, I'll definitely see it more than once.
But Flushed Away has neither the sheer joy of Wallace and Gromit nor the intense motivations of Chicken Run, and I can't help feeling that it's the fault of the villain.
Ian McKellen (whom I ADORE) has done a great job with the voice of the toad, but he is still a small, petulant, STOCK villain.
(SPOILER--Seen Antz? Then you've seen his entire plan already. Get 'em down to the Great Opening Ceremony and flood them out. Phhht.)
He is motivated by a petty sense of revenge, and is not a big enough villain for a really good movie. Mrs. Tweedy, with her arrogant ruthless chicken-exploitation leaves him a mile behind in the dust, and at least General Mandible was driven by a vision. Toad's reason for genocide is amusing, but too silly to be impressive. A villain needs a certain amount of respect from the audience to feel like a real threat, and Toad doesn't work that up, not even with Ian McKellen for a voice. In fact, the movie seems to make a point from his first appearance that he's a hopeless loser. That's no way to create a good nemesis. The villain needs to seem more than a match for the hero.
The pathos of Roddy's situation as a pet was well and subtly expressed, The continual return to toilet references and humor was not (to me, anyway) as funny as it was meant to be, though the half-time plot was sorta funny. And by the end of the film, it felt as if they were really starting to milk those slugs for all they were worth.
Still, it's as good as any of the competition, and it does have a nice Aardman feel to it. Worth watching!