Barbarian invasion is a solid sequel to an already solid game.
With a good premise of destroying or preserving what you built in the first game Barbarian Invasion has a good head start as a sequel. In addition, many new and exciting features have been added in BI.
For example, religion is now much more important in controling your empire. You can now choose from three major religions, Christianity, Paganism, or Zoarastrianism. If you choose for example, Christianity in a pagan settlement the citizens will revolt due to the official religion being contrary to their own. The same goes if you put a Pagan governor in charge of a Christian City. So be careful of you leaders faith.
Another great addition is the new and improved barbarians which now have an improved city biulding platform and can have larger, and more influential cities then in the original game. Also, barbarians now have horde mode in which they can pick up all their belongings and hit the road until they find a new home (usually in Western Roman Lands.)
Moreover, the game is more fun and challanging in general. The original Rome Total War on hard was still a relative breeze. But barbarian invasion rectifies that situation well and that is one thing that many advanced Total War players will love dearly. (Note: If you are new to Total War play around with Rome first and then move onto BI)
The two drawbacks to this expansion are teh horrible skins on the units and the deduction of over all cities and territories. The skins I don't mind so much but the less cities to conquer and control really is frustrating (With them in I may have given the game a 9.3). Some of the best cities from Rome are now gone (and they still existed during this time period to!). No more Messina, Rhodes, Corinth, etc... Italy, Greece, Thrace (the area above Constantinople) and Egypt really got short changed. So it was this drawback that really dissapointed me. However, other than that it is a wonderful game and the emergent factions and the civil wars really add a new strategic depth to it.
All-in-all, Rome Total War Barbarian Invasion is a wonderful, challanging, and semi-historical strategy game that is well worth playing and is incredibly enjoyable. It is just right for some but it was almost but not quite there for me
-Chet