Knack has not gotten much love from GS, but a 4? Hmmm. I admit it is no AAA title, but I thing 4 is way too low.
I'll try and put this simple instead of a long paragraph.
Pros:
Graphics,Controls, story, Unlockables are nice and bring you back, Co-op is fun, challenging bosses at the end, varied approach depending on how big Knack has gotten.
Cons:
Can get repetitive, not that challenging, but good for younger gamers. Camera angles can get weird at times, but nothing that happens often.
I admit this is no AAA title, but it is fun, and that is what I play games for. It was fun sitting down with my son and playing this game through, and he would put this game on par with Mario if you want a younger persons perspective. Don't listen to all the negative reviews, as it is worth playing.