After reading some reviews for Knack it seems that its suffering from being well... Boring. Theyre obviously trying to go for that Crash Bandicoot style action/platformer style, but its simply not up to the standards of what is quite frankly one of the best platforming series' there is.
I said it when the game was revealed. They need to add stuff into the levels and they need to give Knack "more", so to say, when it comes to the actual platforming. It seems very restrictive too.
Kids will love it, but the people looking for that nostalgic, Crash Bandicoot-like experience aint gonna be the ones talking about it.