The 6th gen is the 128-bit era, this is the time of the ps2, xbox, game cube and sega dreamcast, there was apperintly another console called the XaviXPort but i never heard of it. This era ended arounf 2005 when the xbox 360 came out.
Tenchu series, the game which was released since psx era since newer generation console. The game is about being a ninja whose mission to assassinate, infiltrate, escort people, retrieve thingy etc.
Well most series has the bad review due to the graphic problem (muddy graphic character) especially the series released in XBOX 360. But if you are the one who focused gameplay over graphic, there you go :D
Note: The PS2 games are Tenchu 3 and 4 (tenchu fatal shadows)