One problem i see quite regularly on public Army Front servers is that, after being injured, it is very easy for a player to forget they're low on HP as there is no visual indication you're injured apart from the health bar in the top left of the screen. This is very easy to do in the chaos of battle (especially for new players) and I've done it myself in the past.
I therefore suggest that there should be a clearer indication when a player is injured which doesn't rely on them checking the health bar.
In many FPS games, when a player is injured, the border of the screen will often turn red to let the player know. What i'm suggesting is something similar in concept:
-When a player's health drops below a certain level, a red border would begin to appear on their screen.
-This could scale according to the player's health if desired.
-The effect would last until the player's health has increased above the assigned threshold (e.g when healed by a Surgeon).
-This effect must not be too over the top but just visible enough so it can be seen in a player's peripheral vision.
If executed correctly then i believe this UI addition could be very beneficial to the game