Path of Exile and Call of Duty: Modern Warfare 3
Huh.
Well, I guess the most obvious way this would go would be an FPS loot grind game similar to Borderlands, minus most of the style and humor. Pick a soldier (Marine, Army Ranger, SAS, Task Force 141, etc.) which all start as a blank slate, but with a different position on the skill tree based on what each service emphasizes in its training. Weapons replace PoE's skill gems, attachments like scopes and suppressors replace support gems, and air support like the seemingly mandatory AC-130 replace Vaal gems. Drops include gloves, helmets, boots, belts, flak jackets, and various load-bearing equipment that confer different amounts of protection and spots to hold weaponry. Fight scary Communist monsters, mercenary private contractors, and zombies of various non-white colors in cheesy over-the-top set pieces to a fairly generic action movie score that sounds vaguely like every Hans Zimmer score ever. If you're wounded in battle your character is able to shrug off major trauma in a matter of seconds with incredibly high out-of-combat life regeneration, but you can chug flasks of Mountain Dew Gamer Fuel? Cherry/Citrus for some quick in-combat healing. After fighting through a few fairly short acts you get to fight an end boss that requires none of the skills you've practiced throughout the game and is defeated by a quick time event. After defeating the boss you get access endgame content via mapping, just like in PoE, except all new maps are sold separately as DLC (and cannot be played with your friends unless they've bought the maps too).