I'm really surprised there isn't already a thread on this game here!
Anyway, it's a 2D hack and slash sidescroller with RPG elements and somewhat reminiscent of Odin Sphere on the PS2 (also by Vanillaware).
I'm playing this on the Wii at the moment and I absolutely love it. The game is basically split between two ninja characters (male and female) with different stories and encounters (I'm currently playing as Kisuke, the male ninja).
Progress is slowed by coloured barriers that can be destroyed only when the correct Demon Blade (katana) is obtained (i.e. by fighting an area boss). Most of the time, you're running through the screens collecting items, fighting foes that appear at random and occasionally talking and shopping in villages.
The pace is very immediate and pretty much non-stop. The game's main draw, however is the combat. You are awarded on combat performance and gain XP based on how well you fight (not taking a hit and clearing enemies as quickly as possible, for instance results in higher XP). There are also lots of demon blades in this game, and throughout battle, you have to constantly switch between the 3 you have equipped as they have a tendency to snap. When this happens, the blade has to be quickly swapped out with another mid-battle, giving the broken blade time to repair (sped up by collecting souls from dispatched enemies).
Difficulty is well graded, and can be switched between normal and difficult mid-game, though I would advise against trying to be a hero and starting off on hard: start with normal, get comfortable with the system then step up later.
So yeah, a very fast and frenetic 2D slasher with RPG overtones and using the tried and tested "Metroidvania" mechanic to open up the game and story.
In terms of presentation, the game is flawless. It truly is one of the most beautiful looking games I have ever seen. Some of the screens are nothing short of breathtaking and the score is also very well done (the level theme switches up to a more pacy variant whenever enemies appear, which is a nice touch).
There is an awful lot of dross on the Wii, but the good games are out there, so it's a shame to see a wonderful title like this get overlooked. Do yourself a favour and check it out.
I have Oboro Muramasa, its aces! May get it again if I ever buy a Pal Wii so I can understand what the hell has been going on...
Great game. Lovely combat that captures the elegance of swordplay without having to use motion controls. Very clever!
The story doesn't make that much more sense in English, though.