Perhaps I've missed this, but to my knowledge, you won't be able to get items like in traditional RPGs to upgrade your character's equipment, such as armour? I have this impression because of the pre-defined weapons he has and the use of the rune system which is what seems to upgrade these weapons directly, instead of obtaining upgradeable equipment itself.
You have your bow, sword and dagger.
Each one has rune slots that you can unlock or buy with experience points. Whenever you kill a captain or similar high level orc, they leave a random skill for one of the three weapons.
You can then choose which skills you want to insert in your rune slots, or convert them into exp.
Im currenty going for a stealthier approach, so I use skills that generate focus and heath upon a successfull stealth kill, for example. Other gives you X% more damage while riding, or scares two orcs when you brutalise someone instead of one, and so on
You can also unlock new abilities by completing missions and finding artifacts, aswell as uppgrading your character with more health and better attacks.
There's actually quite a lot of improvements to unlock, but you have to progress in the game to get acess to some of the better stuff.
I just managed to unlock a shorter combo finisher, which lowers the amount of successfull blows needed from 8 to 5. Helps a lot!