For me A halo ODST game where you fight the flood.
concept
PRIORITY ONE
You are a member of an ODST squad sent into a flood infect ship. watching as your allies slowly die or turn, about to fall yourself when near the mid game a spartan IV and several sanghelli are brought in. though the fight doesn’t get easier it goes from a horror to a combined arms working to clear out the flood and get a priority 1 asset before destroying the ship, but not all missions go to plan.
the over arching story would start with an ONI ODST squad docks with Autumn class heavy cruiser that has gone dark. A 12 man squad landing in the rear bay only to find it abandoned most pelicans missing, the escape pods launched. And no sign of life. Your Condor will take off stating they will be back with squads 2 through 5. The first mission has you and 5 other ODSTS heading to the engine room light on combat only a few crew combat forms.
But as the game goes on your allies fall support gets cut off, and things start going down hill. What was to be a rather standard clear the gunk mission turns into a fight to the death with a proto gravemind that has taken over the ship. And to make maters worse 1/3rd of the way through a covenant cruiser docks wit the ship after the same thing you are and slowly falls.
By the end the end of the 2nd third you are alone with nothing but a flamethrower, a few shells in a shotgun and a horde on you. Making a desperate play to reach the reactor again. Just as all seems lost two spirit drop ships will enter view with a swords ship. Your character will try to warn them over hte radio only to get a spartan responding with “We know, we are hear to reinforce and pull you out soldier.”
From this point on you have allies with shields, and even a cutscene where a swords engineer grants you one though it is weak. The mission going from a desperate fight with weapons that barely work to a full on action infantry on the “ground” as you recover the objective, and set both ships to self destruct barely making it out with your allies.