HALO is OSR

search your feelings, you know this to be true

Think about it. Master Chief has limited inventory slots (two for guns, two for grenades) designed to force the player into making interesting choices and tradeoffs. If you pick up a powerful but overly specialized weapon like a sniper rifle, gravity hammer, or rocket launcher then you'll be less flexible in situations that those weapons don't excel in, but if you keep to your solid foursquare meat-and-potatoes loadout of battle rifle and shotgun/pistol you may find yourself outgunned or outranged in a key moment. Sometimes you'll just run out of ammo for the better weapons and need to scrape by on readily available trash-tier equipment like the needler until you can scrounge something better, a design philosophy meant to generate tense moments and force the player out of entrenched habits (or learn why the plasma pistol is actually good). 

Halo also uses a two-track HP system with a large pool of easily regenerating ablative HP and a smaller one representing real injuries, which requires a limited resource to restore. The Chief spends a lot of time exploring ancient ruins, interrupting destructive alien rituals, and fighting eldritch tomb-spawned horrors. 

Plus, you can honk the little horn on the mongoose ATV.

Down/Out/Dead: A Death & Dismemberment Variant

​D&D has struggled to find a good answer for "what happens when my character hits 0 HP?" The original answer "you die" leads to a lot of character deaths at 1st level, and eliminates a lot of potential drama with trying to recover/defend a downed and wounded ally, being wounded and captured, etc., so even groups who are comfortable with a high-lethality game have looked for alternatives. Conversely, many of the common alternatives, such as unconsciousness at 0 HP and death at -10 or 5th edition's death saves make the characters too resilient: character death is technically possible, but you need to work pretty hard to make it happen.

Various alternatives exist: a single saving throw at 0 HP is one perfectly good option. Two-tier HP systems, where characters have a lot of ablative HP (commonly called something like Grit, Sweat, etc.) and a small amount of "real" HP representing physical damage (Flesh, Blood, etc.), with death at 0 real HP, is another good one. Bucklers & Backswords rolls the chance of death into weapon type, which interacts nicely with Elizabethan surgery – in a rapier duel it's quite probably for the winner to end up bleeding out from a mortal wound like Inigo Montoya. Other games have adapted some technology from The One Ring and/or various PbtA-derived systems, where "Wounded" is a condition you can get and "Dying" occurs if you're Wounded twice. The most popular alternative in OSR games however is probably the Death & Dismemberment table.