We scored it 4.5/5, and it has already chewed up more time than we care to mention.
Paradox Interactive is giving people a chance to play before they buy, too. The demo allows you to take control of two of the clans over a 15-year time frame. Very limited compared to the full game yes, but surely enough to convince you how awesome the game is.
The full game is released tomorrow, but the demo can be downloaded now from here: http://www.fileplanet.com/222193/220000/fileinfo/Sengoku-Demo