I saw this with friends, all Muppets fans, and we were all pleased. The story was slight but nonetheless affecting at times. I don't particularly buy the core conflict - if you need money just ask corporate exec Gonzo for it rather than recruit him - but really it's just an excuse to put on a show and never pretends to be more. I think it was a little sloppy to not set up one of the key save the day powers, but the musical numbers were quite solid and I laughed hard enough at one chicken-based song that my mother elbowed me in the ribs. I suspect I will buy the soundtrack at some point.
The relationship plotline between the humans wasn't breaking new ground: Jason Segel's character was codependent with his brother and Amy Adams' character wanted more commitment out of him. She could have used a few more flaws of her own to work through, but nicely her character wasn't a killjoy, was reasonably happy to help, and had her own skills. Ultimately, there's nothing unreasonable about wanting a romantic dinner, some alone time, and some tourism time away from the Muppets and the film respected that.
I'm not sure how good of an entry point this film would make, but for those who are already fans it is a fine return to form.