Everyone looking forward to Knack- it is a really mediocre game. I think you're letting the price justify the purchase.
From personal experience, it is a very repetitive, limited action game. Very few options in gameplay and you do them over and over. The story is very fragmented so it doesn't help the experience much.
I'm not saying it's impossible to like- but I honestly don't know what the appeal is of the game. For me, it was disappointing in every respect except the decent graphics.