Creative Assembly confirmed their new game is a standalone expansion for Total War: Rome II... Total War: Attila forums.totalwar.com/showthread…
I've played this game series since the Medieval Total War (2002), as it's by far the best realtime historic battlefield game (it's not a battlefield simulator, but it's as close as you can get while keeping gameplay fun and exciting... real battles are largely a boring affair for 99% of the time and pure terror for 1% and that doesn't translate into engaging gameplay).
The changes to the campaign look VERY interesting... now you can raze towns and retreat (scorched earth tactics) and if you don't repair settlements, the disrepair will now be reflected in the battles (collapsed walls etc).
Towns and cities are now dynamic... buildings can be destroyed by fire, and poorly maitained settlements will be harder to defend (walls will not miraculously build themselves in time for battle unless you've taken care of that in your campaign management).
The family tree is returning and will carry more weight in campaign as each person will live longer in game due to shorter time period covered in campaign... the campaign centres around defending your faction against the invasion of Attila the Hun, so it all takes place in less than 100 years. You can play as Romans (east or west, empire split by the 400's), Saxons were in demo - but it would appear we will not be able to play as the Huns (I hope this turns out to be wrong, but comments indicate campaigns start before Hunnic invasion and you have to defend your lands against it and the pressures it puts on other factions migrating west from the Hunnic pressure).
The gameplay already looks good, but it should as it's off the back of Rome 2... so it's like the Roman equivalent of Fall of the Samurai (Shogun 2) or Napoleon (Empire) standalone expansions.
Release date still not confirmed other than sometime in 2015.