Blood, Blood, Blood!

screendamage |https://steamcommunity.com/sharedfiles/filedetails/?id=1497792466 (2.382 MB)
[H-BBO] Health-Based Blood Overlays |https://steamcommunity.com/sharedfiles/filedetails/?id=2894851294 (163.700 MB)

Some basic addons that makes it clear to the player when they take damage.

For the first: The blood overlays disappear over time, so they're not permanent or tied to the amount of HP you have. VERY basic, and VERY lightweight.
For the second: The lower your health is, the more blood appears on your model. Decent sized and gives more work to the computer but can be configured to make things less taxing.

These things would be for immersion, as well as telling the player when exactly they're taking damage, because it's sometimes hard to tell during high-action situations.