A tip on making zombies threatening is to make a "rage" system, if a zombie spots a player, it will lumber towards it, but if it gets shot, it will start barreling towards it. also make the zombies have 1.5-3 times as much health as blockheads, and make zombies infect players when they kill.
Due to the nature of the virus zombies just want food, regardless of what source.
If it has calories and is detectable it is eaten/tried to be eaten. They don't focus on humans or animals, they like stationary food, but animals and humans tend to have more calories on them lol. They are complete omnivores.
If they are being shot they should cower away OR be raged, depending on that zombie's pre-zombification issues (most would be blood raged), but that's my opinion. These are still humans but they are just crazy enough to be classified as zombies. They should still have SOME sort of self-preservation because no walking and mobile alive zombie = virus cannot spread easy enough.
The thing about this is that zombies are not suppose to be only scary physically and mechanically; it is suppose to be the fear of them.
Zombies are to be feared and avoided, not hunted.