So, after I spent nearly 400 days ingame, i figured out a few things, that needs to be improved.
1. AI doesn't go on campaign if the factions doesn't share any border. (I joined Roman Empire and we're at war against the Frisii since the beginning, and there wasn't a single battle between us, except the couple of battles, I did. And campaigns get canceled after 1-2 days. Always.)
I thought it might be something with the faction, so I started a new game with Roman Illyricum. We went to campaigns against Dacia and Markomanii, but when only Roman Hispania left as an enemy, they never went on a campaign again.
2. The damage of some weapons needs to be improved greatly. Beilieve me, there is no man in the world, who survives 2 headshots from a heavy pilum.(I had around 200 points on throwing and a Power Throw of 5). Also, bows should be improved a little bit as well. I mean, currently, I can charge towards enemy archers, without using my shield(playing with normal damage and using a Legionaire-Armor), and taking only 1-2 damage per hit. Now, the Lorica Hamata was really not suitable against arrows(I did roman re-enacting for 10 years, we tested this many times).
3. Roman factions could be a bit more helpfull or friendly towards each other. Currently every single game i start ends with "civil war" and it's usually between factions who are at 2 different egdes of the map, and so they basically don't do anything, except doing feasts.
4. As mentioned by someone else, parties eat enornmous ammounts. I had my inventory full of food, went against the Frisii with my 120 men(which seems to be more than enough to defeat their whole army on the field) and we ran out of food after a week or so and foraging doesn't really seem to help against it.
5. I don't see higher level legionaires throwing pila. However it was part of the equipment of a legionaire.
6. I miss the auxiliary infantry-troops.(It's good to have some good cavalry for Rome, tho)