Shogun does the same as any Total War game does, it has a very good fan base just off of TW games, not to mention the many few who tried it, and ended up keeping it (me included) just off a video card purchase!
The game itself, I would have payed easily $50 for had I known about it way before! It truly is a great game, and is very well balanced!
The AI is better than in the past but still fails at siege warfare in some situations. You can assault a fort full of cavalry with nothing but a few archers; the cavalry will just sit inside dying, and will never sally forth when they could easily destroy you.
Attacking it does a lot better; although I was still able to figure out a nearly unbeatable strategy once I had multi-level fortresses. The game is still very, very enjoyable, even from just the table-top strategy perspective.