It varies for every faction.

I have played as them before, and beat the crap out of Carthage with them. It was pretty fun, but there was a lot of sitting around to build up the economy and get rich enough to make a good army.

For Lusotannan your troops will be better in an ambush than they would in a pitched fight, especially against the Romans and Carthaginians, but your better troops can easily match the infantrymen of other nations.
Also, many of your troops might not all be strictly Lusotannan, many could be Iberians, and thus technically "civilized". The Iberian troops are especially useful because they provide desperatly needed cavalry support, but it's up to you to decide if you want to use them or not.
Also, they have no long range missile troops that I know of, so you'll need mercenaries there.