Just improve the models to make them more like zombies like the ones from the first game. The current ones (no offense) look more like people getting high on fentanyl than rotting zombies.
The zombies in the first game were creepy because of their rotten designs and very gore-like details.
I've put images of old zombie designs that were going to be in the game as an example. Although the developers have improved the designs a bit, they still look more like people than zombies.