Ok, I've spent a few hours with it now. Not too far, but enough to get a real feel for the game.
First thing off the bat, the performance, even with AA and DX 11 missing (until a patch...lame), the performance and stability is excellent. No crashes or slowdowns yet, something that plagued Empire for months after release.
I'm also thrilled with many of the little interface and GUI improvements. Much more streamlined, much more appealing, and less cluttered.
Most importantly, it feels like the quintessentially perfect Total War game. I haven't played too far in yet, but I quite impressed and pleased with the enemy AI. Even as an old veteran of the series from the first game, the AI was able to take me by surprise, and flank me, hide troops, and effectively not do TOO much that was outright stupid.
I'm sure there are "gamey" exploits out there, but from what I've seen, out of the gate, Shogun 2 might have the best battlefield AI of any Total War game on release. And yes, I've played them all...in order.
I'm also loving little things like the return of the narrator from the first game, many of the same tracks from the first game, and little things like the pre-battle speeches return, narrated in Japanese (with english subs), all add to a very atmospheric effect.
Anyway, so far so good. I'm thoroughly enjoying it, but have my guard up for any bugs or issues down the line. We'll see how it goes