Roeper puts it better than I do, but I was laughing all through the movie. Its swift, witty and irreverently spoofs the entire genre, while still being part of it. The best part about it though, was that till the very end it doesn't become entirely ridiculous (actually works just as action/mystery movie), but when it does decide to be ridiculous, you stop grinning and just start laughing out loud. A reviewer linked off RottenTomatoes put it best.
"If you see Hot Fuzz, you'll never again watch a Michael Bay film without howling with disrespectful laughter."