I really ended up liking Knack and my 4 year old loves him and will still ask to play it a year later. I definitely agree with the detractors that it was a bit shallow but what was there was fun enough. I feel like its most damning problem was that the vast majority of people here and media wrote it off as a joke long before it was ever playable. I never got the feeling that it was trying to sell itself off as some amazing breakthrough of a game, just something that was on the shelf that was appropriate for all audiences. I'd play a sequel with more fleshed out mechanics and features.
EDIT: I will say I don't think his voice matches the character at all.