I love it that the prince learns and this is reflected by adding verbs to the ui or changes them. A truely novel idea! (at least new to me ;-) )
But I think I ran into a bug. The king said he gave me a chess piece (or pieces) but it isn't in the inventory (and there is still the (right) head I already gave to its owner, the (wrong) head vanished). Even after looking serveral times at the chess game (and recieving the piece in text and animation) there is nothing new in the inventory... (played the web version)
Edit: tried it a second time. Again I didn't get the chess pieces after winning. :(
but I liked the art and the story so far. An excellent game with a very clever gameplay-idea!