They got multiple factions with competing motivations, while everyone else just got one. Rome was, understandably, focused on the Romans.
If you demand absolute realism from your Total War games, you’ll want this. The remake doesn’t just apply to the Barbarian hordes, either: factions all over the ancient world have been altered and adjusted in the name of accuracy. Europa’s barbarians aren’t hordes of savages, they’re organised and disciplined. It was founded by a group of history buffs who felt that Rome’s depiction of the ‘Barbarian’ nations was out of step with historical reality.
Europa Barbarorum is the best mod for those seeking absolute historical accuracy.