Well, Germania is propably the by far strongest of the Barb factions. They are strong for a pretty imple reason, they can easily minimize their losses.
All of the Barb lands tend to be struck by massive Brigant uprisings, these dozen of nakeds/warbands etc will take a pretty serios toll on even the Roman forces, alas the Germans move up their phalanx and give them a good beating.
I even think that Germanian spears can easily compete for the point of the most "cost-efficient" phalanx.

They get very good priests (Wotan is essentially +2 command + a healer which can be backep up by another healer which in turn reduces your casulties by roughly 50%, Freya is nice too, more heirs are never bad, more people arent bad too and you can never complain about a +1 acumen) too.
The mid tier units arent as great, however they do fulfill their role.
Never underestimate the effects of scremaing women, they make Barbs run like peasants and romans run like Barbs, very nice, they can also use their charge to flank persons who are flanking your Phalanx, backep up by the creaming it can be enough to make them rout. Germans also have acces to mtd. Archers (mercs in Gothi and further east) as well as some other decent Phalanxflank protectors.
Their lategame is pretty good, the Gothic Cav. is quite top notch, chosen Axes can ruin anybodys day and you temples of Wotan turn even Spears into nasty persons.