I agree actually. They are not voice actors, they are puppeteers first and foremost. Which is why I always thought they should have moved on to new characters, rather than do recasts. Obviously they did try to do that over the years, with varying degrees of success.
I'm a supporter of both. Without the main cast of the Muppets, they'd die on the vine. That's just how it is. I believe that's why The Jim Henson Hour and Muppets Tonight struggled in the ratings. Both introduced too many new characters while classic ones languished in the background.
But yeah, new characters create new dynamics and they keep the Muppet spark alive.
As for successful recasts, this is how I'd order them:
Fozzie, Floyd, Sam, Rowlf, Dr Teeth, Swedish Chef, Uncle Deadly,
Lew, Beaker, Crazy Harry and Sweetums all seem pitch perfect to me in both voice and personality.
Miss Piggy, Kermit, Waldorf and Statler sound a little different at times and their personalities seem to have become a little watered-down over the years.
Animal seems a little off in personality, but close his voice is near perfect.
Scooter, Robin, Janice, Newsman, Link and Pops sound a tad different but their personalities are close to spot-on.
Of course, these are all fan nitpicks I wouldn't give any of them less than a B. I think they've done a great job. I wouldn't change a thing.