Love the ragdolls and how they react to explosions and gunshots, especially this part:
https://youtu.be/YhwE9k2RAl8?t=15Some more blood on bullet hits would be nice.
Maybe even blood dripping out of wounds for a few seconds (even if it doesn't make sense) while the zombies fly through the air.
Next step would (and IMO should) be dismemberment, 2 steps per arm and leg and 1 or 2 steps head removal (shoot off everything above the eye level).