I should say first off that I needed to switch to my phone in order to play this; I don't know if it's because I'm on Linux or using Firefox, but it held me off from playing this for a few days.
That barrier aside, this was good! It is a little on the easy side, though that makes sense if there are going to be even more castles later, and I appreciate how simple to understand it is. The only significant critique I have is that visually, I feel like there should be more background elements.
The mechanics of the second castle were pretty fun, though I'd encourage more puzzles taking advantage of the fact you can only enter the cannons by manually jumping into them (i.e. have to jump in and launch one time and then needing to use it as a solid surface the other time to turn around). That quirk seemed a bit unnecessary to me at first, but I feel like there are interesting things you could do with it.