Barbarian Invasion is set some few hundred years after the campaign shown in the original and the setting is extremely different. The mighty Roman empire has fractured into two factions the Western and Eastern. Despite still having large territories there are few troops to go around, and there are hordes of barbarians such as the Goths, Vandals and Huns waiting to take advantage of any weaknesses on their borders...
In this game you are given the option of commanding most of the factions present from the Saxons in the far north to the Sassanids (the only faction in the add-on with elephants) in the Middle East. The campaign is more limited in that some factions only need 10-15 territories for victory, but that is not as easy as it sounds. Whereas in Rome Total War most battles might be fought with 1000 or less on each side, in the expansion you can find cities besieged by closer to 5000 barbarians! There are some changes to the game-play - some units can now swim, offering an alternative to losing many men crossing a bridge head on. Some troop types can also form shield walls and 'schiltroms', offering better protection from a head-on attack and the ability to prevent cavalry attacking infantry from the rear respectively. Superior generals can now attack at night, which is not only aesthetically pleasing, but also has some benefits such as archers will be less accurate at night. There are a very large number of new units as warfare has changed a little since the earlier game.
All in all this exciting strategy game is better suited for those people who preferred the real-time battles in RTW to the more drawn out campaign map aspect. The battles are more numerous and often challenging as there have been some improvements to the AI, making it more intelligent than before.
