After playing a lot of hours and beating the game with two of the characters (Knight and Moustache man), I can write a recommendation.
This game is gold. Seriously. It combines amazingly the best of the 80s and nowadays.
The graphics are inspired in the ZX Spectrum, but the colours are used without any restrictions and the results are beautiful.
The gameplay is frenetic, short and intense matches that makes you try again immediately after every defeat. And with every run you know a bit better the castle and therefore you are closer to the victory.
The difficulty is kind of old school, but don't let this put you off, if I can finish the game, you can too. You just need to keep trying.
I can't mention anything negative. Well, yes, one thing: the game is for free and they don't take donations. That really annoys me!