Kermit the Frog, Miss Piggy, Animal, Fozzie Bear and the other Muppets haven’t been onscreen in ages. Their creator, Jim Henson, died in 1990. And Frank Oz, the immortal voice of Piggy and Fozzie, declined to participate. So the challenge Disney has with The Muppets is to show a new generation what the fuss was all about. Slam-dunk. Jason Segel, the full-frontal star of Forgetting Sarah Marshall, co-wrote the script with Get Him to the Greek’s Nicholas Stoller. And that’s James Bobin of HBO’s Flight of the Conchords in the director’s chair. R-rated talent with their hands up the Muppets? Whaaat! Take a breath. The new movie never crosses its PG parameters. What it does, enchantingly, is to set a Muppet fan named Gary (Segel) on a journey from Smalltown USA to Hollywood to find out what happened to our felt friends. Gary brings along his girlfriend, Mary (Amy Adams), and his brother, Walter, who looks like Gary in Muppet form. They need to stop an oil baron (Chris Cooper) from destroying the Muppet studios. Solution? Televise a Muppet reunion. The setup works like a charm. So do the songs, with several new ones by Conchords star Bret McKenzie. Adams rocks out on “Me Party.” And Segel’s heartfelt ballad “Man or Muppet?” deserves Academy attention as the movie song of the year. But it’s Kermie, Piggy and the gang who rightly steal the show. The Muppets slaps a smile on your face you won’t want to wipe off.