The "push the envelope" stuff was MUCH worse in MOz. That "nipple" thing was far more disgusting than the innuendo jokes, ad lib or not. Plus, as Simpsonsy and pop cultury as the film was, there was little hints of Muppet sweetness, and there were some good story elements wedged in there. But overall, it works as an overly long TV special, rather than a full fledged movie.That's another problem, although the Muppets have had that sneaky and clever little level of adult humor, they never went too far or tried too hard to push the envelop like is the case with BOTH The Simpsons and Family Guy, and you have to admit, some of what was in IAVMMCM was somewhat inappropriate for a family movie.
MOz was just gross and dark and depressing. Even the only good song in the film is just abhorrently and uncharacteristically violent for a Muppet Movie. Piggy is quite disturbing as a villain, and not even in a fun way. Some lyrics include "On a Good Day, I'll have you begging for mercy," "You're gonna wish that you were already dead," and "Look for all the gory details on the 10 O' Clock News." I wouldn't have been surprised if she went full blown "Saw" on Dorothy. I've never heard a villain song that disturbing... and it's STILL the best song in the film.
And MFS could have been better with the right director. There were some genuinely funny moments at Covnet. And Gonzo's party. Too bad the rest of the movie wasn't like that.