Halo 3: ODST is a stand-alone expansion of Halo 3. Chronologically ODST is concurrent with certain events of Halo 2 - specifically, the game starts right at the end of the "Metropolis" level of Halo 2. During that game, the Covenant had started a full invasion of Earth and occupied the city of New Mombasa. You take on the role of a rookie Orbital Drop Shock Trooper who is trapped behind enemy lines during a drop and it plays out as a Gaiden Game story.The gameplay is largely a throwback to Halo: Combat Evolved with the less effective recharging stamina, the need to find health packs, no ability to go Guns Akimbo, and as a result the use of a pistol that is actually useful in its own way (Halo 2 and 3 were criticized in that regard). While gaining good reviews, some players have criticized a relatively short campaign.The game also included a second disc that was comprised of the Halo 3 multiplayer (no campaign) with all of the downloadable maps (including three that wouldn't be available otherwise for half a year after ODST's release). In addition, it featured a new multiplayer mode called Firefight where you battled endless waves of Covenant coming after you.
Tropers! We are green, and very, very mean!
All There in the Manual: Everyone who has played Halo 2 and Halo 3 already knows why the Covenant attacked New Mombasa and what they are looking for, but the cast is kept in the dark the entire game.
Alternate Ending: Not quite the ending, but a near-end cinematic will change a situation if you get all the Audio Files and make the Rookie more aware of what is going on than anyone else.
This, in fact, changes the cinematic when you meet Virgil. Instead of Dare telling you not to shoot it, you are the one that makes her not shoot the engineer, and, basically telling him it's safe to come down.
Anachronic Order: The game starts with the squad dropping from orbit and the Rookie getting separated from everyone else. As he chases after them, he finds bits of discarded equipment which trigger playable Flashbacks to his squadmates' adventures. It isn't until late in the game that everyone links back up.
Apocalyptic Log: The audio files scattered about the game, when put together, form something akin to a Radio Drama that describes the fall of New Mombasa from the point of view of one of the civilians in the conflict zone. It was written and developed by the same studio that Bungie employed to create I Love Bees, and is something of a side story to a side story.
Artificial Brilliance: You know the cop in the sub levels that fights alongside you, and attempts to betray you, being a Dirty Cop? Well, it turns out that this cop is one badass AI. I mean, he's been reported to actually Halo-jump out of the way of oncoming melee attacks, and is stated by prolific Let's Play maker SSoPHKC to be "the greatest cop who ever lived."
Badass Normal: All of the ODST characters in the game are distinctly less powerful than Master Chief or any Spartan, but they prove to be resourceful in their own right. Buck jumping on a Brute Chieftan's back and stabbing him in the neck repeatedly comes to mind.
Boom, Headshot: There are two Achievements for shooting enemies in the head. One is called "Boom, Headshot".
Canon Immigrant: The game introduces a new Covenant unit: the Engineers (or "Huragok" in the Covenant's own spoken language). Bungie had been trying to work them into the gameplay since Halo: Combat Evolved, but didn't manage to do so until now. The Engineers have always had a presence in the Halo Extended Universe, but it took design a while before they could figure out a way to incorporate what is essentially a non-combatant Covenant race into the combat-heavy First-Person Shooter series in a meaningful way.
Continuity Nod: Just before the Covenant carrier jumps out of the city, you can see a little black speck approach its starboard side. That speck is the In Amber Clad.
Critical Annoyance: If you take damage, your player character will grant you the pleasure of obnoxiously grunting and panting while their stamina regenerates. If their underlying health bar takes a hit, you'll be granted the further pleasure of a constant beeping sound until you find a health pack.
Dirty Cop: Kinsler, New Mombasa's Police Commissioner. He tries to kill Sadie, arranges her father's death, and then hijacks a subway car to get away safely while hundreds of people are trying to get in as well. Luckily karma catches up with him in the end, and he's literally ripped to pieces when said hundreds of people storm the train.
Disproportionate Retribution: When Sadie and her police friend get to the NMPD building, they meet an ex-cop who, seeing as everyone is going to hell soon enough, has decided to send a few of his "Old buddies" on their way himself.
Marshal: Remember how many times I asked you not to use my half-and-half? And remember how many times you... didn't listen? Jim: Wha- You did this? Marshal: You should have stayed in the elevator, Jim... I wrote! -bang- My name! -bang- Right there on the carton! -bang- Mike: Come on, Sadie, let's go... Marshal: According to his department, I have issues with anger management!" -click- "If I were you... I'd stay right where you were.
Dynamic Loading: The Halo engine has always had this in the "fixed path" variation, but this title plays with it a lot more in the New Mombasa Streets that the Rookie explores. Downtown New Mombasa is divided up into several hexagonal blocks by walls (justified in-universe as being mandatory safety measures to minimize damage in case there is a serious accident on the space elevator) with doors closing off the joining streets to stall the Covenant. The Rookie can trigger a manual override of each door, opening it to let himself through. This is intended to slow the player down enough to let the next section of the city load into memory.
Fake Static: Sadie tries it on her father, only for him to point out it's a video feed.
Film Noir: A huge source of inspiration for the game, as stated by Bungie. The influence can be felt in the game in the way the Rookie interacts with the world by seeking out little clues to give him a picture of what happened when trying to locate his squad, the sense of wandering alone through a rainy city at night, and the lonely saxaphone solos in the music.
Fire-Forged Friends: The entire ODST squad counts, but specifically the Rookie, Buck, and Dare.
Foreshadowing: Bungie got clever with this. First, watch the "Desperate Measures" video, paying close attention to the audio starting at around the 2:20 mark. Then, once that's done, go play the final campaign level, "Coastal Highway". And here you thought Buck's line in the video was just hyperbole, didn't you?
Angry Driver: You put your cleaver through the hood of my car! Jonas: Oh, a thousand pardons. But it was either that, or smash your windshield, pull you out, and make you into kebabs. Angry Driver: What?! No! No-no! Hey wait! Jonas: Then please. Stop honking your horn. It frightens the children.
Heroic Mime: The Rookie, while making the occasional grunt when throwing a grenade, or crying out in pain when shot, never says a single word the entire game.
Heroic Sacrifice: Implied with Jonas. He refuses to leave New Mombasa because he would take up too much room, and flatly insists his life isn't worth 5 others.
Hub Level: After the first level the Rookie runs around "Mombasa Streets", finding beacons that unlock other levels, depicted as flashbacks. Playing through one level unlocks the next one, but you can't go back and replay old levels. The hub also has enemies and terminals which give backstory to New Mombassa.
Lonely Piano Piece: One of the common forms of music during the Rookie's segments, along with an occasional slow saxophone solo, to fit the game's contemplative pace and theme of isolation.
Lower Deck Episode: The game is a more personal story of a squad of EliteRed Shirts deployed for a single mission that spans less than half a day of narrative time, in contrast to the series usual stories of a Super Soldier who alter the course of the war, fights an Eldritch Abomination, and prevents genocide on a galactic scale.
Being a puny human instead of a Spartan supersoldier, your melee attacks do noticeably less damage than in Halo 3 proper. Most noticeably, they are no longer a one-hit-kill against enemies like grunts and jackals.
Because Brutes' energy shields now resist human projectile weapons, guns like the assault rifle are noticeably less effective.
The assault rifle itself has been nerfed so that the game's signature SMG is more effective. Other than against vehicles, there is no situation in which the AR would be more useful than the SMG.
After doing a jump in a Warthog/Ghost/Chopper and crash-landing:
Dutch: Uh, Lord? I didn't train to be a pilot. Tell me I don't have any more flying to do today. (Aerial drone crashes into a nearby statue) Dutch: So, was that a yes or a no? (Warthog/Ghost/Chopper explodes) Dutch: Amen.
Dutch: Well, like the good book says, payback's a bitch. Mickey: I don't think it actually says that, Dutch. Dutch: I'm paraphrasin', ya heathen!
Retcon: The game radically alters the look and layout of New Mombasa from the way it was shown in Halo 2. The space elevator is now on its own manmade island instead of in the city center, the buildings of downtown are more futuristic and imposing, and the massive suspension bridge that Master Chief crossed in Halo 2 is nowhere to be seen.
Them there's Dare. It's suspiciously like a Godspell reference, considering her role in the game.
Sergeant Rock: Buck is a near-textbook example of the archetype. He has served in the ODSTs for a long time with a proven success record. The game even says, "if he were any better, he'd be a Spartan."
Shoot the Medic First: Engineers give its allies overshields. The shields dissipate when the Engineer is killed, so it is in your best interest to aim for them first, making the rest a bit easier. There are achievements both for doing this and not doing it in the hub level.
You're a soldier who gets knocked out on his drop and wakes up hours later, presumed dead by your squad. You must discover what happened via interacting with inanimate objects and dead bodies to find out what happened to your squad. Your mission involves an extremely powerful being who is manipulating events above while dealing with hostile non-humans. ** In some buildings there are simplified Thoth logos on the walls.
The Engineers are presented in this game the same way as the S'pht in Marathon.
Virgil; He is your only companion (as The Rookie) for most of the game. He guides you and tells you the story of what happened when you were asleep in your pod, this is very similar to other character named Virgil from The Divine Comedy.
Strictly Professional Relationship: Captain Dare was once in a relationship with Sergeant Buck, but broke it off because of her work with ONI. She intends to keep things professional when the two are put in the same unit again, but he's openly angry at her and she eventually starts letting her affection show through.
Supporting Protagonist: The Rookie. His story comprises the Myth Arc of the game but he doesn't do much to help the mission until the end, being knocked out and all. It's more the story of the other ODSTs, especially Buck and Dare.
Brutes are noticeably tougher in ODST than they were in Halo 3. This is mostly because their shields now take half damage from human projectile weapons, allowing them to soak noticeably more bullets before going down (the plasma rifle or noob combo still owns them, though).
Underrated And Overleveled: If one stops to think about it, all the characters are this. The main Halo franchise focuses on a Bad AssSuper Soldier who was picked from the best of the best, trained from childhood, underwent expensive and dangerous procedures to enhance his physical and mental abilities, and given Powered Armor equipped with shield technology stolen from the enemy. The characters in this game are...well trained soldiers. They are implied to be incredibly skilled even when compared to the rest of the highly elite ODSTs, but they are not super soldiers. However, the game engine is the same as Halo 3, meaning the ODST soldiers are just as powerful as Master Chief. They lose the shields (but replace them with a stamina system that makes them nearly as durable), and they can't punch through tanks like the Chief, but that's about the only difference. In contrast, ODST NPCs in the other games are nothing to write home about.
Heck, there's one area where the ODSTs even outperform Chief, at least until Halo 4. In 3, Chief is slowed considerably while wielding a dismounted turret, but in ODST, none of the playable characters suffer this speed reduction.
Unique Enemy: The NMPD officer in Data Hive, who is your ally for much of the level.