This is a wonderfully made game (except the ending). They did a bunch of things right to make this game genuinely fun and removed a bunch of gimmicks that other games, like Mario/Donkey Kong have.
For example, there's no such thing as lives in this game. If you die, you restart at a checkpoint, and can re-do it over and over as many times as you would like without losing lives and having to reset. The way they balance this out is by making you lose quills (their "coins"), and quills are needed to progress through the game and unlock tonics. They also removed the useless timer that many Mario games have, so you don't have to rush through levels. You can take your time and explore to find all of the hidden T.W.I.T. coins.
Tonics can be found in the over-world and can be used to make your game easier or harder. If you use tonics to make your game easier, you'll lose a percentage of the quills at the end of the level, and vice versa. This is a great mechanic because it rewards those who take risks, but only makes players who want to make the game easier/safer have to play a bit longer to collect enough quills. Great trade off in my opinion.
They also made a way for swimming to feel good. While I still don't prefer swimming levels, they at least play decently in this game.
That being said, the ending of this game is utter trash. It's next level impossible, and it's an entirely different game. While the whole game is very Mario/Donkey Kong inspired, the last boss level is pretty much one of those ridiculous borderline impossible Mario Maker levels you see online. It's not fun, it's RIDICULOUSLY HARD (only 6% of players have the achievement), but it's just simply NOT THE SAME GAME. It's an entirely different genre just slapped on at the end. It's pretty terrible game design and I hope their next game is better thought out when it comes to the ending.
Not to mention the ending was just.. bad? The story of the game boils down to a couple sentences, and after one of the most frustrating "boss" battles I've ever experienced there was zero satisfaction. Just anger at how stupid hard I had to fight to beat the game.
