Ninja Gaiden Sigma was realised awhile ago, and though you may think it is old (don't worry the graphics are still amazing), I still highly recommend you buy it for there is no other game out there quite like this one.
Firstly. You get to be a Ninja. I know, there are plenty of games out there where you're a Ninja but those ones mostly try to be realistic and are more about stealth than stabbing hell out of your enemies!
Ninja Gaiden Sigma casts you as Ryu, an ultra acrobatic, ultra strong and ultimately, an ultra awesome Ninja. This game comes into the category of Devil May Cry style games as you will fly around the environment, leaping off walls to slice the heads of your enemies. Brutally beautiful is what I'd call it. Every spurt of blood seems to somehow just be beautiful. Maybe I'm just sadistic. =P
The combos in this game are greatly varied and each set of weapons you find all have differing ones, catering to your own personal preferences. Would you prefer the nunchucks for quick strikes? Or the staff for long range sweeps? It's really all up to you.
As you go through the game you will earn money and scarabs which can be used to upgrade your weapons and earn new equipment. Now this isn't a RPG so there's no customization but the vast number of weapons are enough to keep you coming back for more Ninja and Demon slaying.
The story of Ninja Gaiden is rather plain and it really shouldn't be played for the narrative. It is merely played when you are simply bored and want to kick some ass! xD The bosses are fun, the battles even funner and the weapons, well I think I've stressed them enough.
If your into fighting games? Ninja games? Kicking ass? Then this game is definitely for you.