Oh, where do I begin? There's a solid idea somewhere in here, but it was very poorly implemented. The ninja character is kind of cute, and he's got some very basic animations for running, jumping, and spinning to attack. That bit's not bad at all.
The constantly-running-in-one-direction-until-you-hit-a-wall mechanic has been done before, and among all the games I've encountered that are played this way, this one is quite likely at the bottom of the list. What's a little different here is that, when you do hit a wall, you stop. Well, if you're running along at ground level, anyway. In and of itself, this could be very well done if approached properly, but there are a couple of things that hamper it severely throughout the game...
1. Level Design. This starts out being almost okay at the beginning, as you practice timing your jumps, flips, wall jumping techniques, and so on. But there aren't any elements in the very first level that can kill you (more on this shortly). The problem is that the level design gets worse. Spaces become smaller, tighter, and ridiculously frustrating when trying to go in the right direction, or - worse yet - having to wait while you are forced to backtrack an untold number of times just do even *try* going in the proper direction. There's a whole heck of a lot riding on that one button, and it isn't even as responsive as it should be much of the time.
2. Loss Conditions. Well, there isn't really much in the way of variety when it comes to enemies, but that just means that more effort should have been put into them. The humanoids with the wrenches aren't a problem, but the gun-toting ones are complete rubbish. There's no animation to show when they're going to fire, they don't need to reload, and they can fire bullets at ridiculous speeds. Not only that, but they wait until you're right about on line with their aim, making it extremely easy to get killed in such a twitchy little action game. You then decided to mix the worst overall level with a crap ton of these and...POOF! You've got a recipe for the most disastrous part of the entire escapade. Oh wait, I almost forgot to mention the two boss battles! *sigh* Neither one is what I would call particularly well made, but the first one is a bloody cakewalk when compared to the fellow who spits fireballs in all directions. Either he kills you (cheaply), or you kill him (just as cheaply). Not a pleasant ending, I'm afraid.
I desperately need to wrap this up, so I'll give you one final piece of critical feedback before I go. It's a little thing that smart game designers like to call Stage Select. Once you've played through the game, wouldn't it be nice to be able to go back and find those idols you missed on your first run? Oh my goodness, YES! But no, it's simply not an option. If you want to do that, you have to start from the very beginning and play through every single level all over again.
Seriously, if you do nothing else, add a stage select feature that at least lets players who have completed the game go back and try to snag those other medals. Better still, let a player restart any level they have already played through once. And show how many idols the player still needs to collect in each level. You've obviously played games before, so you should already know that something a game like this requires at a very base level is some kind of collection mechanic.
So yeah, in a nutshell, this isn't horrible or completely unplayable, but neither is it very good. You can definitely do better.