There is little known, in English, about this latest game in the series which first emerged 10 years ago, but from the debut trailer in Japan it seems likely that the game is indeed a Wii exclusive, probably because of the Ninja-friendly controls offered by the Wii.
Tenchu is known for its stealth gameplay, and the eerie settings of feudal Japan. It was one of the first ninja games to incorporate stealth, a very crucial aspect of Ninjutsu. However, aside from featuring traditional martial arts battles, the game incorporates elements of fantasy and Japanese mythology.
Check out this rather dark trailer for the Japanese release, currently set for October:
Tenchu 4 has yet to be confirmed for North America or Europe, but will surely only be a matter of time. We're expecting a release around Christmas or New Year.