Cool game! I loved the variety and gradual introduction of new mechanics. It kept me engaged and wanting for more.
I found castle 1 fun. Maybe a bit too easy (level 1-12 was more challenging), but it was quite short so it's perfect as a tutorial. Castle 2 was a lot more fun and I had to try a few levels several times. I think you could go even further with the challenges and make things even harder.
Otherwise, the SFX are maybe a bit too loud compared to the background music. I'd recommend tuning it down a bit or adding a setting menu where players can adjust it themselves.
Had fun with this one. Looking forward to a real though Castle 3 maybe. Cheers!