I want a game that i can knife people in or stealthily kill them

[yog-sothot]

Besides the obvious choices (MGS, Hitman, Tenchu...) you could try Deus Ex, Thief, Uncharted 2... even Baldur's gate 2 as some stealth gameplay (just play an assassin !)

I mean, even in a RTS like Dawn of War 2 you can do stealth kills (with the scouts)

that's a lot of great games actually