Kalendros I think the only way to beat them is using melee and knocking off their helm, then using a gun and shooting them in the head.
I'm not sure if it's just me or not but a possible bug would be that my character runs away a lot and for a long period of time and just uncontrollable, I've died a couple times from this.
The only thing I would like the most is the ability to pick up more ammo clips from enemies with the same gun. Very nice game though.