The German tribes at this time were pagans, I believe. Most druidic stuff was up in Britannia. They also had a habit of nailing captured prisoners to trees as offerings to their gods.
Like other Anons have said, picture that nasty, dark, close-in forest, it's been raining for days and it's muddy as all get out. Your legion, and the others with you, are on your way to winter quarters and are stretched out into a long line winding through this forest. Then these barbarians pop out of no where in coordinated attacks, throwing spears at you and your friends, running in to stab a bit, then running away again. Then they do it again later. And again. And again. Until your whole group is running to get somewhere else. Anywhere else. Your comrades-in-arms are falling everywhere around you, as are the camp followers (wives, families, prostitutes, merchants). Keep in mind, Anon, how the Legions were trained to fight: as a cohesive block, where you formed up and relied on all those shields around you as you closed ranks with your pilum and your sword. This sort of one-on-one fighting isn't what you trained for, while your Germanic foes are more than used to fighting one-on-one without much to weigh them down.
Think about this: You know that opening battle in Gladiator? Where the Romans advance all pretty-like and then suddenly go into Hollywood-fighting? Yeah, that giant melee sort of thing where the unit is all broken up would probably have gone pretty bad for the Romans. The Roman commander who defeated Boudicca in Britain specifically refused to engage the Britons unless they had open clearings and boy, did he cut through them when he engaged.
Actually, that could be another interesting idea. You're in a small garrison when Boudicca gets her rebellion started.