Vincit qui se vincit
The direction and the game design.
The graphics, sound design, creative op, interactive animation, art direction etc...are extremely poor (not bad, just really bland and poor compared to other Kirby's), but mostly importantly the game design is weak, rigid and empty which matches the overall direction. I'm not impress by the laziness in design, concept and structures, the only new thing being mouthfull abilities which are very limited in interactions, dual and evolved abilities not being new. Creative direction is incredibly weak and you can see it from the intro: they used in-game assets for a soundless, effectless rendering, and another example is when you free waddles from cage there's almost zero interaction, animation and noise. Overall the game feels pretty shallow and vapid in it's interactive design the same way, it doesn't feel really good.
Nintendo put very little effort in this game, which you could guess from the trailers, even though their main added value is game craft and design: compared to Tropical Freeze, Luigi's or Odyssey, it's very cheap, when it could have been a new 3D/adventure platformer must-have. It's the old Wii's milking and empoverishment scenario again.
If it was an AA indie game, which it clearly is comparable to, I'd say it's between "meh" and "weak" especially compared to masterpieces like Hats in Time or It Takes Two, except it's sold by a corporation as an AAA.
If I had to compare, if Super Mario Odyssey is the Mozart, Aphex Twin, Snoop Dog of 3D plateformers, Kirby Forgotten Land is the Carly Rae Jepsen but if she didn't even do Call me Maybe.
Nonetheless: great OP, it's like an interactive, animated thread.
This absolutely reads like someone who hasn't actually played the game.