If you haven't picked up an Xbox 360 because of its glaringly obvious lack of stealth assassination games, your reason is no longer valid. Tenchu Z is under development by FromSoftware exclusively for the 360.
Tenchu Z will continue the mythology of the Tenchu universe over at least 50 levels of misdirection and evasion. Getting through them will require mastery of a wide array of ninja weaponry from grappling hooks to explosives. In short, you'll need to hone your finely tuned senses as you advance through the game gaining more powerful attacks and special moves acquired through years ofninja training- you did train for years, right?