Personally I have always found leading Gaulic armies in EB to be a somewhat difficult task, and I think that EB has represented reality quite well, their line troops tend to be high damage-low morale mixtures (Northern and Southern Gaulic swordsmen especially) and they tend to excel when led by a good leader but are unreliable under the command of a green general. On the other hand their higher order troops, the solduros and gaesatae are extremely reliable and usually don’t rout unless the commander has horrible leadership skills.

My usual strategy for dealing with this handicap when using green generals against the Sweboz is to insure that there are plenty of slingers around, weaken their line as it approaches and then once they reach javelin range have all of your units open fire simultaneously, the sheer amount of casualties that it causes is staggering and the morale effect is immense, after such an attack a Sweboz battle line tends to rout just as quickly as a Gaulic one (the same tactic works wonders against other Gauls). Later in the game you’ll want to keep a few units of Gaesatae around just to scare your enemies senseless and to provide unparalleled infantry flanking forces, and I usually use Solduros in the center of the line as they are extremely hard to break, although sometimes I use them to insure that a flank holds though the casualties are noticeably higher. The other nifty trick is to hook your light skirmish cavalry around the enemy’s flank and sit behind them throwing javelins into their backs.

Similar tactics are effective against the Romans, though their armour is tougher so the javelins are less effective, your best chance against the Romans is to always have cavalry superiority and plenty of Gaesatae and if your general has high morale bonuses you can defeat just about anyone.

(sorry for any misspellings I’m writing this at 2AM)