Kopikatsu: Actual ninja, but not Naruto ninja.
Flailing Escapist: The only Splinter Cell I haven't played it's Conviction and the ones of the PSP, I highly enjoyed Chaos Theory. Anyway, thanks for the suggestion.
Particulate: Although it would be great to see a ninja game as realistic as ARMA or Operation Flashpoint, I know it wouldn't have a mayor marketing group. I mean seriously, who here has played Way of the Ninja, or actually brought it? and that's a stealth-ACTION game, it's not realistic, but still it's enjoyable.
And well, when I say realistic, I mean in the way that almost every ninja game it's about killing demons and having supernatural abilities. I'm not saying Assassin's Creed it's realistic, but it's far more realistic than say, Shinobi (although, they're not the same genre)or Tenchu (The many deaths of Onikage and Rikimaru).
And of course, if we're going to talk about historical accuracy, a ninja should look like a peasant (or a "shady" peasant) and instead of a sword, he would be carrying farming tools to do his killing, since it's hard to imagine a peasant having enough money to be around using shurikens and swords.
Someday I'll try Thief, since it's been cited as one of the most difficult stealth games, but not now since I know it has monsters and some other stuff I wouldn't be enjoying now.
Thanks for the info everyone.