The game takes a few hours to master the controls, but then it's pretty intuitive. A 'short' campaign takes about 20 hours of playing, depending on how automated you allow it to be. I haven't yet played to the point of world domination, but intend to this time round. It takes a long long time, and I find that I slowly get into the rhythms of long term relative peace and intense periods of movement and death. It's a game you get into far enough to decide whether it's worth it in your particular circumstances to embark on the full thing.
A turn or two a night is usually quite manageable, especially if, like me, you only fight out the larger or otherwise most interesting or vital battles (allowing the computer to simulate the other combats).
The battles happen too quick - something like a half hour. You really have time only to form a plan and then try and stick to it. I suppose that is in some ways 'realistic', but you don't get the hours long ding dong affair that used to occasionally happen in the game's predecessor - 'Medieval: Total War'.
Of course, it's only a substitute for a well run miniatures campaign. Maybe that's why I've refused to part with those couple of legions of 15mm republican roman armies that I acquired in my early teens ...
3 hours ago