Dan Settembrini’s review published on Letterboxd :
Let me start of by saying that I couldn't be more disappointed with this movie. One of the worst films I've seen in years. And I've been forced to watch Transformers: Dark of the Moon. This installment was a train wreck. Which is a shame, since I really enjoyed the previous film. They should've kept Jason Segel as a writer. The previous film was a feel-good movie, this installment was dreary and terrible.
The songs. All the songs from the previous film were absolutely great. All these songs were dull and not memorable. And it truly wasn't that funny. And the accents in this film. They're SO awful, which is a shame because I love Tina Fey. She's awesome. 30 Rock is one of my favorite shows. Let her use her own voice. Don't make Ty Burrell a French officer. In addition, none of the human characters interact with each other. They're in their own subplots, merge them instead.
And in the last scene, there is some of the worst compositing I've ever seen. No spoilers here, but there's a part where there are some people on a wall, and it looks SO BAD. Did they go over budget? Or do it last second? HOLY CRAP it's terrible.
In summation, I really hope the next addition (not confirmed, but I know they'll make another- it's Hollywood) is as good as the previous Muppets movie. Cause watching this made me depressed. Come on Disney, I know you can do better.