Not the good kind of hard.
Don't get me wrong, it was still really well made, but the fight with Tenguman is fucking impossible. Just one hit from him takes down about one fith of Fireman's health, while it takes a million hits to take him down. His dash attacks are almost impossible to read, and his wind attack'll automatically kill you if you're anywhere near the edge of the ring, and you NEED to be right at the edge of the ring in order to hit him.
Also, not a big gripe, but it was kinda weird to see sprites from nes games coinciding with altered sprites from a playstation game. Even though the playstation ones had been redone to look more 2d, they still didn't seem to fit in with the rest of the world.