The general consensus is that any Muppets movie is better than no Muppets movie. And that's where _Muppets Most Wanted _seems to have fallen on the scale of appreciation: it's any Muppets movie.
But I never enjoyed the maudlin, mawkish side of the Muppets ("Rainbow Connection" has always disturbed me; a frog singing about lovers connecting and young sailors called by sweet sounds?--shudder). The 2011 reboot was fully invested in that sentimentality and quite frankly bored me. What I loved most about the Muppets when I was young wasn't their gentle Sesame Street personas, but rather the absurdist showbiz parodies on display in The Muppet Show. It was farcical, sardonic, and felt (at least to my elementary school self) vaguely countercultural--particularly for the late-70s, when the counterculture had fallen so far out of favor. _Muppets Most Wanted _excels because it eschews the schmaltz in favor of that old formula. And that's why it's so much more entertaining than its predecessor.
Much of this has to do with your music, Bret. And though it seems, both demographically and constitutionally, that I should have been a huge fan of "Flight of The Conchords" - the musical comedy duo of which you are (apparently) the meeker half - I never really caught on to it, and instead, each time a friend sings the refrain from "Business Time," I can only pretend to know it. Call me a philistine, but I'm not a fan of (or terribly knowledgeable about) musicals.
But I loved the music in this flick. While there's no centerpiece tune like "Man or Muppet" (your Oscar-winning ditty from the previous Muppets film), there's a consistency in mood and tone in the musical numbers, and they all serve a purpose within the world of the film; they are mechanisms to move the plot forward rather than interstitial flourishes of costume and production design. I guess what I'm trying to say is this (you'll have to interpret this uninformed bit of praise): it felt as if every song was the right length and in the right place.
It's hard to choose a favorite. What should be the weakest song is instead the strongest. "I Can Get You What You Want (Cockatoo in Malibu)" captures everything wonderful about the glittery, narcissistic, post-Disco era in which the Muppets first thrived. Constantine, the criminal mastermind who has usurped Kermit the Frog as leader of the Muppets in order enact various high-stakes robberies, sings the soft-rock ballad to woo Miss Piggy. He promises her satin pillows and armadillos, ice cream cones and mortgage loans. It's the exact kind of aimless and incisive comedy that makes the Muppets great.
Other highlights include Tina Fey introducing a double-crossed Kermit to her Russian prison with the musical number "The Big House" (with backing vocals from your Conchords cohort Jemaine Clement, along with Ray Liotta and Danny Trejo, who seem to be slowly morphing into the same person). "The Interrogation Song" is a fun little bit of staccato sing-speak featuring Ty Burrell and Sam the Eagle - the odd-couple cop-team - trying to extract information from the oblivious Muppets.
The music is really what holds the film together. As the plot bounces us from European city to European city, from Siberian Gulags to Spanish catacombs, from one Kermit to another, from awkward celebrity cameo to awkward celebrity cameo, your music works hard to keep things in harmony.