Well Done
Well, I will basically list everything I liked and noticed about this game- since I have some time to kill and I think your work deserves some effort on my part as well.
I enjoyed the way you introduced the player to the controls and gave them minor tips to aid them while playing the game, throwing them in to the actual game, but somewhat walking them through it. The gameplay of Knights Castle is a nice, easy way of going about playing the game. The fact that you can start this game up and just play adds to how good this game really is. There isn't any complicated details, but just basic fun.
I found the way you went about making the fighting system nicely thought through and put together, though, from the looks of the most recent reviews, a few might of missed it. First; the timer on every one of the spells. I loved it! It made you have to adapt to the situation at hand, while not allowing you to use a certain spell as a crutch throughout the game. With the option of using a certain spell out of question and a wave of creatures coming closer and closer, you had react and find a way to combat them after you just used the last of your larger attacks. Second; how you spaced out the ability to learn different spells and the introduction of new and stronger creatures was nice as well. I noticed that, if you put thought into your decisions involving the spells, the game goes much smoother for you.
Oh! I almost forgot one thing, though. The knight could be just a bit faster, since the timing of hitting some larger enemies and running away is almost not possible with the knight's speed. Well, it isn't anything that important, but I thought the little could be a little quicker is all.
Honestly, I think the people that are complaining about the gameplay are really missing out on what this game really is and what it aims to provide the player with. Well, that is my opinion, though- but, oh well. Well done and thank you for making this game for the other members of Newgrounds to enjoy!