Deerstalker Games has an excellent review on this. I was gonna post my notes here, but considering their review just kinda went over everything, I'll just second all of their claims.
I continue to be disappointed in Hello as his 3d games just do not recieve the same amount of polish as the 2d ones. If you're gonna make a 3d mario game, the main focus should be on movement and making sure the engine feels good. That's should be the main focus, but right now it seems the focus is on more levels, which is a shame cause of the very flawed physics. They have not changed since Prism and they desperately need to be fixed. Mario feels incredibly slippery, jumps feel off, animations look weird, sound effects are too loud, really questionable level design and so on.
It is incredibly frustrating that despite the constant feedback criticizing the physics, nothing gets done about it. And nothing has indicated that things are going to change. It is really important to get playtesters to play your game especially if it's one like this, but this feels completely untested.
So first step in fixing this game would be to go over the suggestions given here in this comment section and then hardcore study the physics of the 3d mario games past 64 to learn what they did right.