Gore should stay realistic.
I actually think the blood in ROOST was well done, it's not an over the top amount of blood that comes out, as others have said gunshots dont always bleed like crazy.
Stuff that i would like to see is more varied wound-textures for explosions, as right now we only have two skins for blown-up people, one for the Russians and one for the Germans, and they are always the same.
A few more 'hitzones' would be very welcome as well, not always taking off just the lower leg, but maybe just a foot, or the entire leg, etc.
More bits and pieces coming off instead of just the same few parts over and over again.
Heads should not explode, but heavier rounds should be able to take away parts of the skull.
And bullet holes in the body ala Rogue Spear would be very, very great as well.
It's always nice to see where exactly you hit somebody
The most important part for me is variation though, and realism.
Variation should come from the expanded hitzones.
Maybe if you hit someone in the jaw with a heavy round his jaw can get shattered, if you hit him in the right side of the forehead that part of his skull comes off a bit, and blood runs over his face.
And if you shoot someone in the throat, he could make choking noises like in Hidden and Dangerous 2. It always gave me a creepy feeling to be shot and fall down on my back, looking at the sky listening to my character choke on his own blood, without being over the top.
And maybe the occasional artery hit could spout a little blood, considering the main artery is always under a fair amount of pressure.
Sometimes the blood reaches the other side of a room in such cases,though i wouldnt suggest putting that in HOS because it would look fake i guess
And as i said earlier, more sections for the limbs to be torn off instead of just the lower leg or arm every single time.