For those complaining that Gonzo didn't get enough screen time, I'll defend the amount of time he did get for this reason.
Throughout the 90s, Gonzo had basically become the lead Muppet. With the unfortunate passing of Jim Henson, and reduced time for Frank Oz, Dave Goelz' Gonzo was basically the last full time Muppet from the big four (him, Kermit, Piggy, & Fozzie). He was most prominent Muppet in all 3 of the 90s Muppet films and even had Muppets from Space be all about him. And I haven't seen all of Muppets Tonight, but from what I recall, Gonzo, Rizzo, Statler, & Waldorf were the only regularly occurring characters from the old crew as the rest made special appearances while the show focused on a load of newer characters like Pepe, Clifford, Bobo, Andy, Randy etc.
Basically my point is, I love Gonzo to death, but I had my fill of him in the spotlight and it is nice to see a return to prominence for Kermit, Piggy, Fozzie, and even Rowlf & Scooter who were basically retired after Jim Henson & Richard Hunt's deaths.
Gonzo had his big moments, and that made me happy. I'll be honest, the scene where The Muppets go to pick up Gonzo might have been my favorite part of the movie. It was weird to see Gonzo acting so professional and then dump all of that to become the wonderfully wacky Gonzo we all know and love. We also got to see him do his Trumpet gag in the Muppet Show theme, which was great.
And without spoiling it, the payoff to the bowling ball gag was fantastic. When they were singing the finale, I was sitting there thinking "That can't be the end!" and then Gonzo's pay off happened and I was like "YES!"
So yeah, Gonzo did just fine in the movie and I was happy with what they did with him.
As for Rizzo? I have no idea why his role was almost nonexistent. I THINK he was the small Muppet sitting on top of the opposite end heavy looking beam that Amy Adams carried across the screen and I saw some Rats skating around, but Rizzo was never specifically referenced or acknowledged in anyway, which was disappointing. Granted, I was happy to see some of my old favorites who haven't had time to shine in while (Rowlf, Crazy Harry, Uncle Deadly) get there couple of moments, but it felt wrong giving a scene to Pepe, Lew Zealand, & Beauregard and not Rizzo.