I thought this was the best game in the series by a mile. There were only two things I didn't like -
1. The campaigns take waayyy too long. Maybe it was just because I chose a really tough one (Three Visits, and I didn't even end up getting Zhu Ge Liang) and played it on historical/advanced, but it must have taken me 80 hours to finish that beast. I wanted to play another campaign with a friend and it was just impossible - having two people sit there for 100+ hours - half of that being the other guy's turn - just isn't going to happen.
2. THE MUSIC - if anybody anywhere is threatening one of your borders, the battle music plays. Since this makes up 75% of the game once you've got a decent sized empire, you spend hours upon hours upon hours listening to that one 3 minute song. After a while I had to just turn the sound off - that song is still burned into my brain.
But other than that, it was the deepest game in the series, the integrated world view was great, the visuals were really nice, they FINALLY found a way to make naval combat matter, and I liked that town building wasn't just a menu option ("build economy" etc.).
Best turn-based strategy game on the PS2 or Wii, it's just a shame that the series is apparently done. At least Koei's bringing over the most recent Nobunaga game next month.