This was a really good game for what it is. It's reminiscent of NES platform fighting games, but it has save points at reasonable places, upgrades to find - the stuff you'd expect in a modern game. It also has better, catchier music than most modern games have. A lot of the bosses are very cool looking. The graphics are intentionally retro, but given that limitation they look good.
On the other hand, it also has a melodramatic plot (although you can ignore that), and toward the end the game just gets a little TOO hard. But to be fair, even when things are really, really hard, MOST of the time it's a matter of figuring out what to do, meaning how to best use your various abilities to make the situation more manageable. So for most of the game, I didn't mind having to restart sections over and over because I felt like I was making progress by thinking things through. But in the rare times when it really does require precision (and in the many times when it seems like that's the only way to win), it does get frustrating. But none of this makes me dislike the game overall. (I paid the $15 pre-order price; the regular price is probably reasonable too if you're into this genre - I don't actually have any nostalgia for the NES ninja games.)
There was also one design bug, which I found quite frustrating. There's this part where you have to climb a set of platforms faster than this spirit monkey thing. The game hints that you can make it easier by sword-bouncing off of these lantern things, but I had this power-up left over from a previous area that made a blade spin around me and destroy stuff. That's great when you're fighting enemies, but this thing destroyed the lanterns before I could approach, so I just had to do the whole thing with very precise jumping. Drove me crazy.