I don't think Metallica and medieval warfare mix very well. If you want metal (which I appreciate) what about something more epic and appropriate? Gothic, Viking, Pagan or Folk for example.
The vid itself is a bit... well, we don't see anything really. Just a huge bunch of soldiers (such huge regiments look odd to me), hardly organised in any way, clashing together. We neither see who fights against whom (Obviously the teutonic order against... ?) and why.
What I mean by saying "why" is that if you play a game, just record it while you're playing and in the end play some music not related to the game or setting in any way it kinda gets boring for me (personal oppinion). If you want something unique then think of a kind of script. Think about what camera angles would look cool in which moment, try to capture some of the atmosphere right before the battle or the aftermath. You have to work with actual video editing in this case but there are lots of freeware tools which feature at least basic editing techniques you could try out.
The idea is good, but it takes quite some time to create something worth watching. Your video is (again, personal oppinion) more or less just a bunch of units hitting each other while the camera randomly zooms in and out the carnage, and when you just look at the game without being able to play it I think it's just a bit tiring. With some editing and a script however, such a battle can equal a small machinima project and could be very much fun to watch.