For 4 - worth checking out Squad. 50v50 matches with quite a bit of realism baked in. My favorite moments are getting setup in advance where the enemy is likely to advance with a trusty MG, going prone and just waiting for them to run into my sightline.

While having quick reflexes is always a benefit, positioning and teamwork is more important in Squad.

Finding a server with consistently decent squad leaders is definitely important to get the most out of the game. If the squad lead isn't talking for more then a minute or two, leave and join another.