Gonna repost this from the "review-proof game" thread, since that was mostly dead.
To be honest, after starting my playthrough of Knack on Hard, I'm surprised at how low it scored. It's not a platformer, but it's not exactly a straight brawler either.
The main focus of combat is to reach your opponent without getting hit, or getting hit as little as possible, and while the game provides you with very few moves, they all have specific functions and specialties, as well as weaknesses. You've got to figure out which situations call for which kind of moves, then employ them as the battle calls.
For instance, certain moves like the aerial roll attack have a dangerous amount of recovery time attached to them. It should only be used when you're fighting an isolated enemy, and only when you are close enough that you're sure it will strike. Also, you must note that the attack does less damage than Knack's basic ground combo, or one of his dash strikes. However, being in the air is arguably one of the safest locations Knack can be, as he can avoid strikes from most enemies.
All of this comes together into something like a reflex puzzle in each scenario. You may argue that there is no progressing moveset, and while that is mostly true, I think the real progression simply comes from the new enemy types you have to learn how to handle with the tools you have.
I think someone could argue well that Knack isn't a badly designed, game, but people are going about it the wrong way, or they're making the wrong arguments. The children angle by itself is weak. There's challenge to be had in Knack, and while it's simple at it's core, it is far from brain-dead.