Put simply, not bad at all. The story itself is timeless, especially since it draws heavily on the Cold War and simply puts a kid-friendly face on it, and while the CG looks pretty blatant, the filmmaker's decision to use a mix of animated, animatronics and real animals in the film means there could have been a lot more scenes that simply didn't look right in the higher resolution.
The basic premise of Cats & Dogs is that there has been a long-standing war between our two favorite pet species, and while we knew of their animosity, we had no idea just how far this skirmish had escalated. Ever since the dogs freed us humans from feline rule in ancient Egypt, they have seen it as their job to protect us from the cat menace, and a vital key to that protection might be just around the corner.
Professor Brody (Jeff Goldblum) is on the verge of developing a formula to cure dog allergies for good. With this in place, dogs can be everywhere and protect their friends all the time. When the professor's undercover agent, a long time agency operative named Buddy, is captured, the secret underground organization needs to put a new set of paws in the house. Unfortunately, the puppy that gets chosen isn't one of their trained professionals. Its a beagle named Lou (Tobey Maguire).
At least Lou isn't all alone in his newly discovered mission. He is joined by the neighborhood's leader, Butch (Alec Baldwin), former agent turned stray, Ivy (Susan Sarandon), the jumpy and tech savvy Peek (Joe Pantoliano) and a sheepdog named Sam (Michael Clarke Duncan). It seems that the mission to protect the professor isn't going to be all fun and games. In fact, there is a mastermind feline looking to make sure Brody's formula doesn't see the light of day, and this evil Persian goes by the menacing name of Mr. Tinkles (Sean Hayes), not to mention his sidekick, Calico (Jon Lovitz).
As the story progresses, Lou tries hard to stay on guard, but he finds the young boy of the family, Scott (Alexander Pollock) in need of his love and attention. Much to the dismay of Butch, Lou starts to play with the boy, and while there are a few bumps along the way, a particularly painful one involving a Russian Blue cat, you know it will all work out in the end.
Like I said, the story does a good job spanning the near-decade of time, and for the most part, the various visual effects still look good. The various commentaries talk about everything from training the live pets, to using the animatronic puppets, to making the pets talk with CG, a practice that wasn't done all that well, and can now be seen in an unknown number of Air Bud/Buddies films.
While re-watching Cats & Dogs is a good idea if you are planning on seeing the new film, buying it isn't really necessary, and, quite frankly, neither is seeing it in high definition. While the picture is unmistakably more crisp, some of the off-colored or not-quite-right lighting that comes with CG mixed with live action is much more obvious on Blu-ray. I've liked this movie for a while now, but unless your kids get really into the film, its more worth a rental rather then a purchase.