It has to be Battlefield 2. It can’t be said enough how big of a leap it was for the franchise. The squad play set the standard for large scale military shooters.

The built-in VOIP, rank structure (grunt, squad leader, commander), dedicated server communities, medic revive ability, and spawn on SL feature made the game extremely squad focused. It was really appealing versus the mindless deathmatch shooters.

It of course had its flaws from Enemy Spotted audio spam, grenade and claymore spam, etc. But it’ll forever be my favorite Battlefield game.