I played this scenario twice with my wife yesterday. Since it's a short one we changed sides after the first one.
1) Rome - Gauls: 4-1
6 cards vs 4 for Rome is huge, but the main advantage for Rome is starting first.
Mounted charge and it was already 2-0 before I (as Gaul) even blinked. I almost lost Britomartus along with his cavalry but he managed to evade to warriors (the other cav died as well).
The next couple of turns were me struggling to kill some Romans while surviving at the same time. I managed to kill one cav (general survived) and that was it, 2 dead Auxilia it was romans' easy win.
2) Rome - Gauls: 4-0
Crappy card for me as Rome (so no Mounted Charge) but still I managed to smash gaul center and wipe out one cav. Britomartus again survived. The next couple of turns were mostly light infantry and auxilia exchanging ranged hits and me trying to reduce warriors to 3 attack dice. There were some close calls but Gauls didn't kill any roman unit (evade for the win ). "Outflanked" and "2 units left" mopped up wounded Gauls and that was that.
Overall, it's a VERY one sided scenario. Gauls simply don't have the answer to Roman MC (especially with commanders either attached or adjacent) and auxilia is quite a liability since it can't evade and is densely packed. It's definitely not a balanced scenario and aside from some godly cards and luck I don't see much hope for gaul army. However, it's quite nice for playing both sides in one session because it's fast and simple.
Mounted Charge for Rome out the starting gate, even a First Strike by Gauls did not counter. They Darkened Skies to weaken most Roman cavalry but the Romans reached their 4 banners before Gauls could exploit all the weakened cavalry targets.