Agreed, but you have to give Williams his due - he completey became Sy, until I almost forgot he ever did Mork or Popeye or Mrs Doubtfire, but then I watched the extra features, and it all came flooding back to me. I love him as an actor but can't always understand why he does some films (Bicentenial Man?)
Personally, I would say that unless you love Robin Williams, you should rent this one before you buy it. The ending does stink.