Let's say that you were given a list of animals and you were tasked with writing out the attributes most commonly associated with those animals. If you put down that lions are regal, that wolves are vicious, or that hummingbirds are fast, no one would argue with you. On the other hand, if you put down that frogs are leaders, that pigs are jealous or that dogs are musical, people would wonder what in the hell you were talking about.
But when it comes to the Muppets that's exactly what you get. Kermit the Frog is the frazzled leader, and Miss Piggy is insecure, and Rowlf the Dog is good at the piano. I think it says something about the people behind the Muppets that you could easily have switched around the puppets and still have made the characters work. The Miss Piggy puppet might not have been the best choice for the consistently overwhelmed ringleader character because her face has thick cheeks and thus has less flexibility, but beyond that, you could make any number of substitutions and the jokes, characters and stories would still work. If the Swedish Chef had been a bear in a funny hat would we have ever thought that was weird? Because it's not any weirder than thinking that a bear in a funny hat should be a bad stand up comedian.
Once you start to notice little details like that it becomes a lot more obvious how unconventional the Muppets were. Some of their quirks stand out immediately, of course; they always did a lot of meta-textual stuff was pretty daring for such a kid friendly vehicle. However, some of their other more subtle touches are easier to miss. For example, the Great Muppet Caper is about a team of supermodels turned jewel thieves who try to break into London's most secure vault to steal a legendary diamond, and they don't make any references to James Bond (who is after all the go-to guy for supermodels, supercrooks and Briatain), but they do find time to do a Busby Berkeley style aquatic dance number. Once you realize that they follow their muse to where it takes them, even if that place isn't the most logical or current place to go to, then the decision to throw a Gonzo in with a Swedish Chef in with a bunch of barnyard animals starts to make a bit more sense. Clearly, this is a world where the common denominator is a gentleness of spirit, not any sort of real world equivalency.
That gentleness writes a pretty big check, artistically speaking. Unlike a lot of kids movies in the post-Pixar world we live in now, this is a kids movie that feels very much like a kids movie, so judging it critically seems unnecessary. Yes, the Great Muppet Caper is pretty ramshackle, with huge stretches of the movie forgetting about the jewel thieves entirely, but there's no reason why it should have to conform to the rigid narrative structures of an adult story as long as it remains entertaining. While there are setpieces that work better than others the Great Muppet Caper is always pleasant, and that should be enough. I mean, that frog already works for a newspaper and plays a banjo. You can't seriously expect him to schedule his adventures to conform to a three act structure, too!
Winner: No Contest (I slept for a bit towards the end; not a judgment on the movie - I'm just very comfortable with this movie, which I've already seen a bunch.)