First, commanders. The Romans are cursed with a terrible bunch of generals. You'll be lucky to find somebody with more than 2 points in either offensive or defensive abilities. There's only one Roman general that can be favourable compared with the Cantabrian and Asturian chieftains, M. Vipsanius Agrippa, and he arrives so late in the game that the scenario is almost over by then. So for most of the time, you'll have to manage with less than stellar commanders. On the other hand, the barbarians are blessed with magnificent commanders. Corocotta and Gauson, the two most important ones, are both brilliant generals and it's very hard to beat either of them decisively. The lower ranking barbarian commanders are also generally better than their Roman colleagues.
Second, terrain. It's very challenging to fight the Cantabrians and Asturians in the mountains. They have excellent infantry, and combined with their mountain bonuses and excellent commanders, even the best of your legions are in trouble when fighting against them. The legions would have at least some advantage in open terrain, but there's not much of that around the victory locations.
Third, logistics. It takes time to besiege the mountain strongholds, and sieges can drag on month after month, unless you get lucky and breach quickly. I don't know how the quality of the commanders affects this, but I wouldn't be surprised if poor quality commanders make it harder to get breaches. So you'll need plenty of supply wagons to keep your armies in supply. However, the wagons are emptied quickly, so you'll have to send them to friendly areas for resupply. This is dangerous, because you can't detach too many troops to guard the wagons, which are in danger of barbarian attack while moving between your armies and bases. Achieving balance in this business is hard to do.
Poor Roman commanders and brilliant barbarian chieftains leading troops in advantageous terrain means that you can very easily lose even big battles. This is problematic, because a single major defeat in pitched battle can make you lose a huge amount of national morale. Once Corocotta, the Cantabrian military genius, won a major battle that caused heavy casualties to my legions but also to his troops. I ended up losing something like 6 or 7 points of morale, which felt excessive. A couple of such defeats means that your national morale quickly goes so low that it makes it even harder to win any battles with inferior troops and commanders, which again lowers your national morale. I'm thinking that maybe this is too excessive in this scenario.
Playing on the barbarian side, I was surprised to see how easy it was. I almost felt sorry when Corocotta and Gauson gave the Romans one whipping after another. It got me thinking that perhaps it's too easy to create and maintain big Asturian, Cantabrian and Iberian armies in this scenario, or that their cooperation is too effective. As far as I understand, they weren't a very centralized civilization, which always helped the well-organized Romans in their battles against the so-called barbarians. Maybe there should be maluses for creating too big and mixed armies of various tribes?
Anyway, as the Roman side you really need to capture the barbarian bases as quickly as you can. Perhaps your only advantage is much bigger income and thus the ability to recruit more replacements. The barbarians can't keep suffering excessive casualties for too long, because they'll run out of money and replacements. But making that to happen is far from easy.
It's definitely an interesting scenario and well worth the money. I've spent a longer time playing this one scenario than many full games! BOR and AJE are absolutely excellent investments.
