It's great to hear that theme and see the add'ua logo. I still get tingly at all teh Tenchu series openings. I am also one of the few who liked 2, but I did miss music in the levels (other than user-created, those had short repeating tracks).
Plus, the revelation on winning as Tatsumaru is pretty cool. Great FMV.
Get Tenchu 3, it follows up directly to part 1 and should be pretty cheap.
Asakura also did guitar work for Rurouni Kenshin, which is why some of the Tenchu music sounds like it is using samples from Kenshin.
There is a girl in the trailer, a boss I guess, who uses a combination crossbow/twin wrist blades that looks just like Hyuakurin's from Blade of the Immortal.