There's not much to do in the demo, you get to play a tutorial of the campaign map which is alright I would have rather they gave you only one faction to choose from and only let you play a certain number of turns since I already know how the campaign map works.
The demo's historical battle is nasty and you play on the side that historically lost... You start with the larger force but your allies don't help you they just sit there and wait then one gets involved but has a very small force (Which came in handy for me), then shortly after the other allies join in but... they turn on you and they have a large army. I knew that was going to happen, I've read about the battle and watched a program about it, sucked though.
I got slaughtered the first time I did that battle, even before the allies turned, my enemy rushed me and I wasn't sure what was going on or what units I had were. I just played again today and made a much better go of it, I won but not by much.
Graphics, they aren't a great improvement, the samurai are hard to look at they are very dark and their armour is shiny in an unnatural way. I think the demo is of an early build because in the options not everything is there yet. AA for example isn't there, and there are some texture options that have high but not very high. It's also a bit more of a drain on this PC this time around, I was getting between 30 and 50 fps where as on Napoleon Total War 40 was a low point with AA on full. Again that could be because it's an early build, they might have optimized it for the full release. It's also a different culture and geographical position from the last TW game so I might just need to get used to the difference.