The expanssion pack looks good
1 - it's called RTW: Barbarian Invasion
2 - it is set in the years 364 to 476 AD, with the Roman empire split into East and West
3 - you can play as either "wing" of the Roman empire and start with a fully formed empire. Your object is simple - survive! The barabarian hordes and lots of rebellions to fend off it says.
4 - There are several barbarian campaigns - Vandals, Saxons and Huns are named
5 - There is a rival empire - the Sassanid from Persia
6 - the Huns have no settlements at all and start with "15 large armies" and have to sweep across the map
7 - there are lots of new units and tactics: a type of x-bow unit, Hun lancers, barbarian Golden Band (elite berserkers), mobile chariot artillery, the Shiltrom (a kind of barabarian phalanx), a shield wall formation, morale boosting druids and priests are all mentioned
8 - there will be spectacular night time battles where morale of the defenders will be lower at the start (tho attackers' morale can drop it seems if they don't break through!)
9 - river battles will allow some light units (inc cavalry!) to SWIM across and avoid "death at the bridge"