Totally fun from start to finish, although I didn't play the second story yet.  The pacing of introducing new concepts and testing you on them is nice and brisk, and keeps the game exciting, even if you have played hundreds of similar games before.  The trade off is that the game is quite short.

The difficulty was a bit too hard for my 3 and 7 year old children, but for someone who has played 2D platformers for decades it was pretty easy.

Controls are great but I used a 3rd party tool to map my gamepad to the Crowtel's keyboard inputs.

Not as good as classics of the genre like Cave Story or Kero Blaster.
If you are spoiled by free flash games 5 dollars will seem pretty steep, and obviously something like Hollow Knight ($15) will entertain you for far longer.  But in a world where "Clash of Clans" developer Supercell made 810 million in profit, $2 billion in revenue in 2017 without even releasing a new game, I've been trying to buy more full priced indie games almost as an act of protest.