I thought it was pretty enjoyable overall. It really did feel like they had the tone of the classic Muppet Show down for the most part (with a modern twist of course). Perhaps just nitpicking, but I would've preferred they did it like the original series where the guest star performs in the second number and the closing number. I also think they should've had more spontaneous sketches without a Kermit introduction.
One thing I think they actually improved on the original series was having more scenes with the actual audience members. Maya Rudolph felt most at home with the Muppets of the 3 guest stars. And on that note, I hope they stick to having one guest star like the original if future installments are made.
As far as highlights go, I really loved seeing Muppet Labs, Sam playing the bartender in the Sabrina Carpenter number, and Gonzo doing another daredevil act. Felt like a callback to the Lou Rawls episode (in which Fozzie couldn't control his roller skates) when Gonzo kept zooming around the theater. And Beaurgard messing things up as Rizzo performed "Blinding Lights" by the Weeknd was excellent, perhaps a nod to the Joan Baez episode where he befriends the rats. Also some little tidbits here and there were fun, like Pops sleeping in the theater box, Hilda having a line for the first time in half a century, and Janice getting a backstage scene.
A small compliment, but it was nice that they had a full end credits sequence that matched the original series, as most modern shows have ditched that at this point. I'd probably give this special an 8.5/10. A little rough around the edges, but a strong return to the classic format nonetheless. And hats off to Dave Goelz. We are so incredibly lucky he is still performing his classic characters.