Not that great to be honest. It sort of tries to be a parody of light-hearted family-friendly films but ends up becoming one itself (if you forget about the couple scenes of flesh eating violence) It also doesn't go anywhere with the zombie thing either. It's like they were so in love with their own idea of making a story about a boy and his dog.... except instead of a dog, they use a zombie, that they really don't do anything else with the concept. Instead of making any attempt at actually being funny, they just keep going on with that dog metaphor for the entire movie, hoping that that by itself will be sufficiently funny. The problem is it starts to get old part way through, and you sort of wish they would do something unexpected with it to rise above the cliche' but they never do.
Now, don't get me wrong, it's not a horrible movie by any means, it's actually fairly decent. Good for a rent, but don't expect too much from it. It's actually something that you might like to watch with your kids, if you don't mind them seeing zombie-violence (which is used sparingly and is nowhere near as graphic as what you would see in a Romero zombie movie)