THE FINE PRINT OF THE STANDARD "RICH AND FAMOUS" CONTRACT: Let me get the obvious out of the way first: The Muppets, and the Toy Story short which precedes it, is a joyful romp. It gleefully mocks one's efforts to impose the standards of realism upon it while landing joke after joke, and even if its "are we too earnest for this era?" questioning is a bit strawmanish ("strawmanly?") it nevertheless will hit you in a place that is warm and fuzzy. Or Fozzie.
The note I want to add is that part of what the film does is absolutely confirm my Unified Muppet Theory -- that while The Muppet Movie tells the "true" story of how these performers came together and formed a troupe, each of the subsequent films (as well as "The Muppet Show") is a fictional work created within the narrative universe of that film -- namely, The Muppets Take Manhattan and the like are the films being created under the terms of the Standard "Rich and Famous" Contract.
Oh, those terms. Indeed, The Muppets returns to that original narrative. This is the movie about what happened to that troupe after decades in the limelight, after starring in those films and having all those famous people show up on "The Muppet Show." It is premised upon the details of that Contract upon which Kermit failed to perform due diligence, highlighting the importance of hiring top-notch attorneys to protect one's intellectual property. And in the end (and this can't possibly be a spoiler), it sets the terms in the fictional universe (as well as, hopefully, our actual one) by which these characters can now go back to making whatever future silly films they want.
Also, it has Mickey Rooney. And fart shoes!