Microsoft's running a sale on Mark Of The Ninja for Xbox Live right now for 600 of their imaginary Microsoft points, or about $9.90 in real world money. If you're an Xbox 360 owner, why are you still reading this? Go and buy it NOW!
The PC version of Mark Of The Ninja has gone on sale via Steam a few times, so it's perfectly valid to buy that option instead. Either way, this is a top-notch game. How good? It made my own personal top ten list of 2012 over at Kotaku. Or in other words, you have my personal recommendation on this one. Trust me. [Xbox]