It's looking pretty good, but you're right that it still seems to be missing something.
The glossy/shiny "manufactured" finish is maybe what's distracting. Needs to be less shiny, more dirty and weathered and distressed.
I think a couple thin strips of gauze, loosely pasted onto the surface would give you a start. Don't layer up the gauze, you want your paint job to be visible through it. Make sure to fray and shred the edges first, then don't lie them down flat like you would do paper mache, let them fall unevenly, not completely adhered to the mask surface. Maybe as that's drying, sprinkle it with some powder to give it a dusty, matte appearance? I don't know how well that would work, test it on some scrap first.
Then some blood made from acrylic paint (as opposed to corn syrup or other foodstuffs), flung onto the mask from a distance, not brushed on, so you get odd splatters. You might hang up the mask/helmet together with the rest of your outfit when you do this, so if you get long splatter lines they "match up" from the mask to the rest of the outfit.