Very well made but..
I just don't buy the premise. In the previous films we've seen marines, special forces and all kinds of trained fighters with modern weaponry trying to take on the Predator and fail. How are we supposed to believe that a bunch of medieval warriors with swords and crossbows stand any chance?
The film was very nicely made,most of the actors were good, some of the characters were memorable and the footage taken from previous films was well integrated visually and story-wise. I dare say that it stands above many AAA studio productions in some aspects.
I think that an interesting idea would be to have the Predator be less advanced itself to "match" his opponents. For instance, the plasma caster was just a cheap trick in these battles. Maybe he could have some sort of advanced mechanical spike launcher (operating like his blades), to be in similar footing with the (cross)bow bearers.