A surprisingly well integrated story and great variety make this game a must play for stealth action fans. Spoiler Free
And there is still good reason to keep playing the game which is another fantastic reason to own it. Your hero is a member of a ninja clan that accepted the enormous burden of being given the gift of great power at the eventual expense of his own life. He receives these powers via toxic tattoos and as the game progresses so does your quantity of both tattoos and their relative powers. The story involves a nameless rival corporate army that is led by a goofilly written spoof on every corporate big wig bad guy from every 80's movie ever featuring one. While being very silly the game does a great job of making fun of the stereotype. The ninja side of the story is much different and by the final scene you are genuinely torn by a difficult choice (although in subsequent play-throughs the "correct" decision was more apparent based on foreshadowing and plot dialogue).
Being a stealth game there is the obvious play with light and shadows to look forward to. What is surprising is how often you can use light to your advantage if you choose to. And the final levels make fun use of light in the puzzle mechanics.
The game controls beautifully and moving quickly and silently from perches to vents to dark corners at the tops of walls becomes an absolute delight because of it. As you complete level specific objectives you open up gear and combat abilities as well as "paths". Paths are different ninja philosophies and each has it's own outfit (One cool thing you will notice is that the ninja on the title screen is always wearing the last outfit you had on and the animations are quite good). The standard path is the Path of the Ninja which enables you to carry one attack and one distraction item (such as a poisonous dart and a smoke bomb). After beating the game and then beating the new game plus option (which makes the game more realistic and satisfying by limiting your vision to your line of sight and removing the sound/vision indicators from you and your enemies) I had a great time playing through on the Path of Silence which takes away all of your weapons but allows you to carry two distraction items. This was by far the most challenging and rewarding way to play since it is a lot easier in many cases to thin out the ranks or kill a pesky guard that's in your way than it is to distract them or sneak by. You can also play as a terror, a melee expert, a stealth killer and one I'll leave you to discover as it would be a bit spoilerish to tell you.
There are quite a few different level specific goals to look forward to. Many of them help you to learn how to get the most out of your equipment or are even designed to help you get achievements. There is also a score goal and three scrolls to find in every level. The scrolls add a nice bit of story and are mostly told in Haiku. Obtaining all of the scrolls requires the most subtlety and dexterity out of your character and also involves the Challenge rooms. Every level has one which holds one of the three scrolls for that level. One minor complaint is that the challenge rooms weren't very challenging. They seemed mostly designed to help you understand a puzzle solving concept or maneuvering challenge. The game already does a great job at feeding you concepts. So good in fact I remember likening it to Portal's wonderfully paced difficulty and concept introductions.
The environments are as diverse as you can expect while making use of the same basic maneuvering options such as grapple points and vents. The latter third of the game brings in many more environmental hazards and the enemies in the last two levels can be quite tricky on new game plus...although you do have a sweet new tattoo ability to look forward to for those sections.
When everything comes together and you're flying through the darkness inches from death in every direction this game is as thrilling as Assassin's Creed or Rainbow Six in it's stealth predator feel which is amazing since it's a pretty simple 2D side-scroller. It has diversity, good story, excellent controls, great artistic design and excellent replay value. You should not miss this game.