I just read the two reviews on Aint It Cool News and they do contain several spoilers so I'm probably gonna stop looking now.
The word is that the movie is filled with Muppets, that there are some great musical numbers, there's classic rapid-fire humor throughout the film, it's not too heavy-handed with the cameos or human stars, Jason, Amy and Chris do a fantastic job, they don't waste much time getting into the action, it comes in somewhere around 100 minutes and leaves you wanting more. I don't really need to know more than that.