When it comes to replacements I have mixed feelings. For me, the voice is important, but so is personality.
When it comes to Piggy, Fozzie, and Animal, Eric has the personality AND the voice whichmakes him perfect.
Scooter being done by Brian has personality and a darn good voice, so he's my fav for Scooter.
Now the Swedish Cehf being done by Bill is another huge hit for me. Personality and voice from what I've seen.
From what I heard in the Weezer making of clip with Rowlf, Bill hasn't seemed to capture the voice that well or the personality. He was too much like Bobo. And when Pepe was finally off screen, Rowlf talked about him. Rowlf wouldn't have done that I think.
Kermit is a bit tougher for me. I definatly miss Jim's Kermit, but I also accept Steve's Kermit as the character. I think with Kermit being a radical change hurt the transition process for all. With Scooter, he was silent for so long I think people are way less critical of Brian. Chef is a fairly easy voice so that helped Bill a lot I think. And of course who can beat Eric's Piggy, Fozzie and Animal besides Frank himself?
Anyway thats just how I look at it.
Oh! One more thing. Statler. Statler has not been the same since Jerry took him over. he doesn't sound right, he doesn't look right now, and the interaction between Statler and Waldorf isn't as good either. As you all know, I think Steve captures the look, the personality, and the voice. But I think I've stated my opinion on Statler more than enough times.