Just a stunning adaptation, plus Curry
Even if this did not have Curry in it, it would still have been a good adaptation of Stevenson's story. The muppets do the muppet-thing and it is silly, and funny, and light. It is just a good movie.
THEN you add Tim Curry to the mix and you get something... remarkable. The meme "The reason Michael Caine and Tim Curry are so good in their respective Muppet movies is that Michael Caine treats the Muppets as fellow actors, and Tim Curry treats himself as a fellow Muppet." He fits well in with the rest of the cast, the manic energy matches the lightheart...
