Ninja Guardian is a lot like Machiavelli's Ascent (which we reviewed here), only with Ninjas. And smaller. The game screens are each divided into three panes, each textured to look like canvas. When not in use (i.e. a game screen or some sort of message), each screen sports a Hiroshige-styled Japanese landscape painting. While playing the game, the center 1/3rd of the screen acts as a platforming bounce-field. Depending on the level or game mode, you get a certain number of double-jumps (allow you to jump in mid-air) and shuriken shields. For the most part, though, you'll use the left stick to navigate left or right to various types of platforms (clouds, tree branches, even enemies) which allow you to continue your rise.
While the endless mode is exactly like Machiavelli's Ascent (with the aforementioned powerups), the Arcade mode guides you through a series of pre-constructed levels that each have a finite ending at the top. You progress from the ground up through a variety of levels until you reach the upper atmosphere, where you do battle with a giant floating demon head. While I did enjoy the arcade mode, I wish it were longer (I think it took me around 10 minutes).
I have three major complaints with Ninja Guardian. First, I'm not sure that the extra powerups actually add anything to the gameplay. The style is great (and completely different from Machiavelli's Ascent), but the gameplay is actually worse. In the midst of a 10-bounce combo, your main character is moving a little too fast for you to also worry about whether you need to block incoming projectiles or press the attack button to bounce off of the enemies. Some of this probably could've been mitigated if not for problem number two: the game is small. Really small. Actual gameplay is confined to the middle 1/3rd of the screen, and the main character is a tiny fraction of that height. If I had a hard time making out what was going on with a 50 inch HDTV, playing on a smaller screen is probably a lot like playing pin the tail on the evil samurai warlord.
My final complaint is a little more minor, and has mostly to do with how menu interactions were handled. During arcade mode or while entering scores on endless mode, the game would often just "end." The level would be finished, but nothing would happen. Only after staring at the screen for a few moments would I notice that the far right 1/3rd of the screen (which isn't used for anything during gameplay) would now have a "press 'A' to continue" message. While I could probably get used to doing that eventually, the stealthiness (stealthy... like a ninja!) of the message was a constant source of annoyance the whole time I was trying the game. This problem isn't unique to Ninja Guardian, but it should be codified somewhere into a game design law: "If your players needs to do something to advance a screen, you'd better be damn well sure they know what to do."
All in all, Ninja Guardian isn't a terrible game--it just doesn't add a lot to the mechanic and can be kind of hard to play at its size. For 240 points, I'd skip it and grab something else.