Now, don't get me wrong. I am not saying this depth is exclusive to Ninja Gaiden. Nor even video games. Nor is this the only (or even close to the biggest) reason I love the series. It's just a small aspect of it that I find to be really cool and part of the reason I keep playing after all of these years.
And for my long time readers, yes, I am still yammering on and on about Ninja Gaiden. It will never end so