Overall: We enjoyed it. The Muppets were good and they didn't spend much time on peripheral Muppets, which I liked. I was never a hardcore Muppet fan; I liked Kermit and Miss Piggy but didn't really watch the TV show. Gasp, I know; am I even an American?!
It was less heartfelt than The Muppets, more of a madcap comedy but well-done and enjoyable. Pretty clear what was happening at all times; only really young kids may get a little confused.
Music: The music was good, much like the first Muppets reboot. Bret McKenzie did a great job with the songs, I think. I wasn't sure if he was involved with this one until one of the songs started -- I think it was "The Big House" -- and I thought, "That sounds a lot like Flight of the Conchords." And sure enough!
Cameos: I know people love cameos but I felt like some of them were just distractions and didn't add anything at all. Except Tom Hiddleston wasn't in it enough. Honestly, I didn't realize who he was at first; he is one of those people who can look drastically different from one role to another and in this he does not resemble Loki at all. I would say that's a good thing since this is a kids' movie but he plays a criminal in a Siberian gulag, so... In general, though, I'm always ready for more T.Hid.
Acting: Tina Fey did a good job, funny and pretty consistent with the Russian accent. Ricky Gervais was okay but it seemed like he has decided he is a little too cool to enjoy being in a Muppets movie. Not too cool to be in one, especially since The Muppets did so well, but too cool to really enjoy it. I don't know, maybe it's just the way he interpreted the character he was playing, but it just felt a little flat. As far as I'm concerned, the movie's saving grace was Ty Burrell. He was completely entertaining. Not only was he consistent and funny, but it seemed like he was genuinely having fun. Like he was thinking, "I can't believe they're paying me to do this!" Not like he signed on because The Muppets did so well but because he just thought it would be a hoot. Ty Burrell FTW!
Takeaway: If you have kids or just love the Muppets, it's worth watching. Two frog legs up!