Console launches are not known for the quality of their titles. Except for the occasional anomaly like Mario 64, launch games are largely testbeds for new tech. Games can be underwhelming technically, but sometimes experimental in terms of new gameplay. Knack is the exact opposite: it's a game that's intended to "wow" visually, but is the most basic of experiences.
In Knack, you take control of the titular character who happens to be a collection of swirling suspended polygons. As the character, you will move along a linear path, while dispatching with small groups of very similar enemies. Knack will knock enemies unconscious by either punching them (Square while on the ground), doing a seeking aerial attack a la Sonic (Square while in the air), or using a super move if you have enough gems or whatever. There's a dodge system too, but none of it feels particularly satisfying. Knack is never nimble, the enemies are repetitive, and with no gamewide progression, everything gets old fast.
That being said, Knack can absorb more "artifacts" to become larger, which is an interesting experience. The mildly frustrating enemy you had faced previously now seems so insignificant when you're four times your original size. The ascension and first few minutes of this experience are great, but the stripping away of these powers and the restart of the buildup cycle is demotivating. Metroid games wouldn't have been enjoyable had Samus experienced the inverse Deus Ex Machina of losing all her items on every level. Game designers can only use this dramatic reversal of competency to punctuate a particular story beat. The eternal yo-yo of power that is Knack should be remembered as an ultimately unsatisfying experience.
This thinly veiled physics engine demo would be bearable had it not the personality of corrugated cardboard. None of the characters or story have any heart; they're forgettable people acting in forgettable situations to a forgettable soundtrack. It's a direct-to-DVD children's movie that allocated too much money to producing high-poly, well-textured characters based on composite images of crowd characers from Cloudy with a Chance of Meatballs.
I'm sure there are people who liked Knack, but one might be able to explain that on scarcity of games that arguably persists to this day. In the future wasteland, irradiated water is still water, and Knack, despite its flaws, is still a game that people could play with their launch day PlayStation 4s.