Just finished Katana Zero. It's a very good game with a great story, only downfall is how short it is. I'd still say it is worth the dosh to pick up. It's kinda like a Ninja Gaiden x Hotline Miami.
and it is really not that hard, all the people complaining about the difficulty are likely retarded or game journalists, in which case they are already retarded. I beat the initial game in about 6-7 hours. Again, it is a short game, but the flame that burns twice as hot looks really ****ing cool and is a ton of fun to play with. Isn't that how it goes?
oh, and the music is incredible too...