Some suggestion:
1st
A "gun" (an item like a main/secondary gun) that allows a player to heal a teammate
it takes away fire power in order to help the team
maybe you can gain 5xp for each heal?
Problem: easy xp farm
Maybe its too unbalenced and annoying/unfair
2nd
An ability like "vulture", each time you kill and enemy a percentage of his like his restored to you
(ex: you kill a guy with 100hp you get 25% back to you (25hp), 50hp->12hp and so on)
3rd
instead of a "weapon" smth like a Pack that you can lay on the ground for you or a team mate to pick up, like on other fps like battlefield
4th
After a while without sustaining damage the player's hp begins to regenerate (like stamina) never getting to full again obviously
if you have any doubts pls ask here in the comments
Actually idk even know if these are good ideas, i see loads of pros and cons, PLS let some commentaries below
Great Suggestion Stereben!
You could have some pros fighting on offense, but some of the weaker using those heal guns on them when the get into red or yellow hp. The only problem is that it'd make that team supperior to the other and annoy them really much. So i'm not sure about this.....