* ClicheStorm: The story's a simpler retelling of the first game and it shows. The heroes, tired from losing battles against the Covenant, fight them for a map room that points them to another place. They fight some more, get to the other place, and find the bad guys are going to use an ancient construct to kill even more people with. So they blow it up and float in space. Also the Flood's there.
* ComplacentGamingSyndrome: Good luck finding someone online who doesn't attack with Spartans in Scorpions.
* DemonicSpiders: In ''Halo Wars'' multiplayer, Gauss Hogs are this, with Gunner/Grenadier Hogs only being GoddamnedBats.
** In the campaign on [[HarderThanHard Legendary]], Hunters are the 'bane' of your existence. Especially your Scorpion tanks. [[BlatantLies It gets even better]] that they tend to come fully upgraded.
* FridgeBrilliance: Look closely on the visors of the [=SPARTANs=] on the cover, and you'll see the Arbiter and Elites. The Limited Edition cover shows the Arbiter and Elites. They're facing each other.
* GoodBadBugs: The unfinished Scarab can't kill units in cover, as hard as it tries. Put some Marines in the Covie guard tower in the middle of the map and you'll have the Scarab distracted for the rest of the level.
* MemeticMutation: [[http://oi40.tinypic.com/9sqwjq.jpg HAAH WAAW]]
* ThatOneLevel: Arguably every mission following Relic Interior can fall into this category on higher difficulties, namely Legendary. Often because of a [[ScrappyMechanic frustrating gimmick]] the AI ruthlessly exploits.
** Arcadia City forces you to play defense and offense as well as babysit blink-and-they-die transports. Every now and then a wave of fully upgraded Banshees bum rushes the transports. It's especially jarring when you lose them thanks to a [[TakingYouWithMe kamikaze]] Banshee.
** Arcadia Outskirts has you [[HoldTheLine play defense against a lengthy Covenant Assault]]. A Covenant [[FromBadToWorse Mega Turret]] joins in the fray with an almost ungodly Rate of Fire, forcing you to divert units that would otherwise be fending off the swarms of Covenant Soldiers to take it out... and then watch them explode in-route from the said turret.
** Dome of Light brings wave after wave of Covenant forces to your base to keep you from planting 5 mildly durable tanks. It's insanely difficult to protect the [[DemonicSpiders Hunter]] flooded base and still guard the tanks, even using leader transport powers tends to barely finish the mission.
** 'Scarab'. The titular Covenant walker tank acts as a stationary turret tearing through all your troops. If you take too long it's game over, and it can take a hell of a beating. To get the gold medal you almost have to glitch.
** Anders' Signal. While the rest of the mission you can [[TakeYourTime take as long as you like]], the beginning part is absolutely nightmarish trying to keep your [[ClownCarBase Elephant]] intact from the hard-to-kill Brute Choppers with nothing but un-upgraded basic squads.
** The Flood. If you thought those space zombies were hard in single player, try fighting a whole army of them ''while'' trying to destroy their colonies to weaken their largest one. Did we mention that the colonies regenerate if you take too long to destroy them all?
** Shield World. [[ZeroPunctuation Yahtzee]] rage quitted on this mission for good reason. A race against the clock to rescue your platoons trapped behind Flood-infested lines of endlessly-spawning flyers and loads of artillery with little time in the beginning to build your forces before the first platoon gets overrun.
** Repairs. The dropships start coming faster and faster and faster and faster... [[FromBadToWorse And eventually the Covenant destroyer joins in.]]
** Reactor. Surprisingly not as intense in the beginning as the Covenant, Forerunner Sentinels, and the Flood are more interested in killing each other than you, but take too long and the Covies will churn out a [[SpiderTank Scarab]] to hunt your reactor down.
* ThatOneSidequest: 'Running The Show' achievement requires a million points in multiplayer. This is reduced from the original three million. This represents literally hundreds of hours of play.