These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The revelation that Hicks is still alive, having been abducted from the Sulaco by Weyland-Yutani, and that the corpse recovered in Alien³ was apparently a body double. This revelation is handwaved by the character as being a "much longer story". Assuming that the corporation was able to find the Sulaco and find a suitable body double for Hicks, why would they go to all the trouble to abduct one person? And while they were aboard, why didn't they take Ripley, Bishop (who is their product, and could give more information on the mission) or Newt (who was the only survivor from the colony) with them too?
Voodoo Shark: The explanation (what little we get) makes even less sense than the event itself does.
The notion that the Boilers are blind. Xenomorphs don't have eyes in the first place.
Critic Proof: In spite of the largely negative response to the game, the title was still the 26th best-selling video game of 2013.
Disappointing Last Level: The final level (and boss battle) of the game involves Winter running around the cargo bay of Michael Weyland's personal ship as a xenomorph queen chases him around. While you still have all of your weapons, you cannot make a dent in her with any of them - you must run around the deck and activate a series of switches before using the final one to (attempt to) knock her out of the cargo bay doors into the upper atmosphere. Fans hoping to have a retread of the Ripley/Queen powerloader fight from Aliens are likely to be disappointed (although a similar scenario appears earlier in the game when a loader must be used to defeat two Ravens).
Goddamned Bats: The Weyland-Yutani PMCs have impeccable aim and can kill you quite quickly.
Narm: The Boilers are blind creepier-looking Xenomorphs that can walk right up to you and explode. It's too bad that when they walk up to you, they do this◊.
Never Live It Down: People are already using the Never Trust a Trailer mentality that this game brought about for the game's pseudo-sequel, Alien: Isolation - even though Isolation actually had a playable demo and is being made by a different studio.
During some footage shown at E3 and in the demo, there is a sequence in which, while you and other marines are fighting the xenomorphs, a massive Alien Queen shows up out of nowhere, grabs an unlucky marine and rips the poor bastard in half, before it turns to you and charges at you. This is not in the final game.
Something that is in the game, however, is a scene where scientists are trying to calm the angry Queen, which inevitably goes downhill once the power fails. She ends up massacring the scientists trapped in the room with her (leaving blood spots in their wake), and tries to break out of the room to attack Winter and O'Neal.
"The Raven" is the closest the game gets to being classic Survival Horror. Even with the silly Boiler animation, the concept that you could be vaporized at any second can put players on their toes.
Heck, the Raven itself! It kills you instantly if it catches up to you, and at the beginning of the stealth level, you're treated to a close-up of its face. Its not pretty.
The Lurkers manage to create tension when they appear, as they quickly sneak around in shadows and behind cover and try to pounce you. This is one of the few occasions when the motion detector is actually useful.
Sequelitis: Colonial Marines received generally lower scores on average than the Alien vs. Predator series of games (including the 2010 installment).
Surprisingly Improved Sequel: The Stasis Interrupted DLC has generally been regarded as an improvement over the main campaign. Not only does it benefit from the recent general patches to the A.I. and engine, but the level design has also been improved to increase the tension and create more challenging fights, such as by having you have to fight alone for a large portion of the game instead of always having multiple NPCs to draw agro from xenos and mercs, as well as having more open areas where xenos can attack you from all directions.
The Apocalyptic Log in No Hope in Hadley's features commentary by a woman concerning her husband's attack by some thing... And then it turns out that it's Newt's mother, leading her family to the cafeteria. Given what happened in the comic tie-in Newt's Tale, there was only one way it was going to end.
Bella's death, already upsetting as it is, was made worse by the fact of all the measures that Winter and O'Neil employed to avoid it.
Lisbeth discovering her parents' corpses in the "Stasis Interrupted" DLC. Even if she's only a character for a short time in the story, it's difficult watching her discover her father draped over her mother's facehugged/bullet-ridden body, and her subsequent breakdown.
Regardless of whether you think it's Sega's, Gearbox's, or Timegate's fault ACM turned out so disappointing, it's quite obvious none of them put in the effort on this game that they indicated in previews.
A recent notion as of late is that the developers seemingly spent more time cramming as many continuity nods and Easter eggs as they could into the game, instead of focusing on the story and graphics (and some of those Easter eggs had low-quality animation to boot). Notably, the discovery of an Easter Egg on the "Nostromo" level from the Movie Map Pack DLC (and the knowledge that an entire team spent time animating and programming Jones the cat, who appears for all of a split-second in the level) led to people asking why they couldn't have devoted their team to fixing lingering plot problems instead.
They Wasted a Perfectly Good Plot: One of the main criticisms of the game, the titular aliens are only the main enemies for a small portion of the game, and most of it is spent fighting other marines.
Win Back The Crowd: After the backlash for the main game, Gearbox tried to win players back through the subsequent DLC's. Whether they succeeded or failed is still up for debate.
The 4-gigabyte 1.03 patch. In addition to improving many of the graphics in the game, along with adding a film grain filter to make gameplay smoother, the patch reintroduces elements seen in the E3 demo (such as the cracking glass when the Marine hits the Sulaco umbilical in "Distress") and greatly increases the AI of the xenomorphs on all difficulty levels (to the point that the new Recruit difficulty is more difficult than the vanilla game's Ultimate Badass Mode).
The Bug Hunt DLC received a very favorable reception, with the players who were still in multiplayer stating that it was even better than the base game, thanks to its frantic gameplay, new maps and increased difficulty. The Movie Map Pack DLC also got a good response, thanks to being chockful of Continuity Nods and Easter Eggs.
The Stasis Interrupted DLC received a lot of praise for not only clearing up a lot of lingering plot issues with the main game, but also ratcheting up the tension and making the gameplay much tougher. It even had people who were deadset against the game from the beginning praising it for being a step in the right direction.