I'd go with Bornleverpuller and TeddyBhoy,s responses.
Story driven, with objectives opening and closing depending on the previous outcomes. Not something that follows a clearly defined pathway that feels preordained. Surprises and curve balls, like something happening elsewhere impacting on your plans. A defined hierarchy within teams and the expectation that you follow "orders". Although many games involve some kind of special forces team so small units being given a task or series of tasks but planning how they would best complete this by themselves like the "Chinese parliament" often described in SAS books.
Distinct requirements for skill sets, eg dedicated sniper teams, support team, patrols. And games with a pace that allows distinct units to be deployed for particular tasks, not all the time mind. I would not expect a sniper to deployed in the field for the whole game dug in, but potentially I could see someone with sniper kit swapping between their rifleman loadout and their sniper load out as tasks dictate.
Milsim to me would require times of simple admin type activities, guarding a base or check point, but that this could lead to defending bases from assaults. Less breaks from game time, so 12, 24, 36 and 48 hour games with personal admin being completed in games. It being a prop and vehicle heavy environment. But I wouldn't expect people to be humping all of their kit all the time, packs to be left at LUP's etc. A definite kit requirement to fit the time period of the story and team setting, eg SF kitted out as SF would be, Vietcong in black and green.
Battlesim and Filmsim would take some of this stuff but potentially involve a degree of role play, be shorter, perhaps involve periods in game punctuated by out of game, eg 9am-9pm in game 9pm-9am relax and socialise out of game.