Undying Loyalty: The true geth. No matter how badly they were treated by the quarians, even to the point of genocide, they still value them as parents. Given the chance, the geth repay the quarians in a big way, even restoring their immune systems and caretaking their world. There's a certain amount of pain from Legion when he ponders what the geth could do when their own beloved creators wanted to destroy them.
Unobtanium: Element zero is stated in the Codex to be generated only when stars go boom. The primary sources of eezo are, thus, the debris fields surrounding neutron stars and black holes, requiring extensive set-up costs for the telerobotic systems and radiation shielding necessary to mine it. It is also the only means of manipulating mass known. It is thus the rarest and most valuable substance in the galaxy. However, everyFTL craft, everyFlying Car, everyomni-tool and every firearm (not to mention every biotic) has a few grams somewhere inside of it. Not mention, two words: eezo toothbrushes.
Luckily, not all that delicious Unobtanium stays in such harsh places. Good-sized chunks are often caught in the orbits of younger stars, where it can be mined much more easily; Omega Station was the result of one such mine. And the galaxy seems to be filled with Ghost Planets which gathered the material for their own use, meaning Adventurer Archaeologists can make a cute credit or so doing a little Grave Robbing. This probably destroyed most remaining evidence of The Reapers in the process. One could assume that this is the case for all Mass Effect technology; why would a centuries-old galaxy-spanning civilization that uses the stuff extensively everthrow any of it away?
Unusually Uninteresting Sight: Not only doesn't a trio of heavily armored and armed to the teeth soldiers turn any heads, you can discharge an automatic weapon right in the middle of the seat of the galactic government and onlookers won't even interrupt their conversation.
You can also take a geth with you to the Citadel, or a turian or salarian to Tuchanka, without even a pause from the locals.
Averted however if you take Legion the Geth Infiltrator with you to the Quarian Flotilla. They will have something to say about it.
Unwinnable by Mistake: In all three games there are dangerous spots where your character can cross some invisible boundary and become unable to go back, forever hanging in mid-air. In 2 there is such a spot on Alchera, in 3 there is a particularly nasty spot on the Normandy's bridge.
Vicious Cycle: The Reapers wipe out all sapient organic life in the galaxy at least every fifty thousand years or so. They state that this cycle has repeated itself more times than humans can possibly imagine. So, let's just give you a brief picture: there is hard evidence that a Reaper invasion occurred thirty-seven million years ago. Not simple enough for you? Then here's the lowdown: this means that the Reapers have invaded at least SEVEN HUNDRED AND FORTY TIMES. And it's not even the first time that someone tried to fight the Reapers, only to be defeated.
and their purpose is to prevent yet another vicious cycle (i.e. technological singularity) from wiping out organic life full-stop.
It gets worse if the Leviathan of Dis was killed by the Reapers. It is a billion years old by the time of Mass Effect. That would work out to around 20,000 Reapers Cycles.
The third game reveals that The Leviathan of Dis actually is a dead Reaper.
Victory By Endurance: According to the Codex, this is humanity's main method of fighting. Humanity attacks the enemy's supplies, headquarters and resources foremost, leaving enemy forces leaderless with less logistical support until the human fleets can curb stomp them. Humanity's approach to warfare is based on rapid reaction forces which seek to decapitate command and control and avoid attrition while remaining highly manoeuvrable. Mass Effect's codices basically have humanity fighting Third and Fourth generation warfare...in SPACE! The rest of the galaxy has barely managed to catch up to human innovations in strategic thought from about the time of the biplanes. Turians still fight massive wars of attrition. Humanity is always shown as being simply more tactically proficient than everyone else to the point of actually subtly paralleling earth history. As the Turians and everyone else builds Dreadnoughts, humans realize carriers are the future and make many of them. Humans have the first ship able to use "stealth." It bears a striking resemblance to a submarine. Sound familiar? The Turians may as well call their military groups Legions for how "groman" they are. Salarians don't have the endurance that human forces have and the Asari are still fielding armies of light infantry from city-states. Krogan are shown to be poor strategists for a race of proud warrior race guys, and their culture resembles tribes of Maori or African warriors from pre-nation state times.
Also the Virtual Intelligences, humanoid computer programs. Bioware most likely added them so the player could interact with electronics without a bunch of reading involved.
Villain Override: First seen in the original game when Sovereign turned Saren's corpse into a super-Husk. Extremely prominent in the second game, to the point of giving the trope's page quote, with Harbinger and the Collectors.
Inverted when after failing its appointed task, the Reaper Harbinger releases control of the Collector General, leaving it to its fate.
Virtual Ghost: The quarians used to do this, although it was to preserve the knowledge of their ancestors and not to become immortal. They stopped once the geth conquered their homeworld and destroyed the databanks containing them.
the Protheans are particularly fond of this trope.
According to Cerberus News, a ship containing a one-billion-strong race of virtual aliens has made contact with Council space after travelling the galaxy for 8000 years after uploading their minds to a virtual world to save their civilisation from destruction.
The Virus: Again, two to four varieties, depending on your personal criteria.
We Are As Mayflies: Both the krogan and the asari live for about a thousand years, whereas humans in the 22nd century are lucky to live to one hundred and fifty. Inverted with the salarians who live to be about 40. The vorcha, introduced in Mass Effect 2, have a lifespan of only 20 years.
Wearing a Flag on Your Head: More subtle than most instances. This is what most turians do; that's actually what their face-paint is.
...the turian term "barefaced" refers to one who is beguiling or not to be trusted. It is also a slang term for politicians. —Codex entry on turians
We Cannot Go On Without You: If Shepard is KO'd during a battle, you get the Game Over screen (unlike Shepard's teammates, who automatically recover after the fight ends if they were KO'd, even if the Unity ability isn't used).
This trope is acknowledged if you get the worst ending of the second game. Joker also mentions it early on as the reason the team broke up after Shepard was killed - they were Shepard's team. Without him/her, there was no reason for them to stay together.
Welcome to Corneria: Typical BioWare approach. NPCs usually answer the same thing whenever you ask (for convenience). Subverted by/averted by some random NPCs.
Well-Intentioned Extremist: The Cerberus organization, at least if you're human. Except if you're a biotic, or any particular individual, as the survival of the species overrides anything else (ethics, human decency, etc).
At the end of ME3 we learn this of the Reapers. They were created long, long, long ago by someone to prevent chaos. Not the chaos of organic evolution as implied earlier, but the chaotic destruction of organic life by synthetic life. So when organic civilizations become advanced enough to create synthetics, the Reapers come in, immortalize the advanced civilizations as new Reapers, and destroy all civilization, then retreat to deep space to wait for it to happen again.
We Will Have Perfect Health in the Future: Medical science advancements have extended the human life expectancy to around 150 years. Some people still get diseases though. Such as your pilot, Joker, who has a rare medical condition that makes his bones really brittle. Though even that technology is advanced, since Joker said if he was born during our time, he would've died as an infant.
What Beautiful Eyes: The second game really ratchets the visual quality of all the character eyes. Miranda and Doctor Chakwas are two of the prettier examples.
Default male Shepard has striking blue eyes while on the flip side, the default female Shepard has bright green eyes...unless you go renegade.
What Do You Mean, It's Not Symbolic?: In ME2. Shepard dies and is resurrected by the Lazarus Project. Shepard has to head to Omega, enter a nightclub called Afterlife in order to recruit someone named Archangel. With all the squadmates available from DLC, Shepard will have 12. Ringing any bells?
And when you get to the heaven-like planet Illium, there is a bar called Eternity.
Not to mention having to go to a prison named Purgatory.
Which is also a bar!
Whole Plot Reference: Let's see... the human race discovers ancient alien technology on Mars, gets into a first contact war with another alien race, eventually joins a UN-styled space station run by representatives from three major alien races and several minor representatives from others, and eventually the main character (whose initials are JS who dies and comes back to life) steals a massive prototype space ship and breaks away from the government to fight an ancient alien race that resembles a large organic spaceship. Sound familiar?
Don't forget, said organizations sanction a collection of Badasses that are above the law, and only accountable to a couple people at the top.
And the third game is one protracted quest to enlist help from multiple factions who all distrust each other to some degree in order to prevent the fall of civilization at the hands of Eldritch Abominations that can only be defeated through the use of a superweapon of ancient design, all while a secondary villain stands in your way because he thinks he can defeat the Big Bad by his own means. And the hero might end up having to sacrifice him/herself in the end to finish the task I do believe BioWare has been down this road before.
A Wizard Did It: Or rather a mass effect field. Why your squadmates can survive in hard vacuum without a helmet. Probably.
Given that the squadmates who don't have helmets are nominally biotics, such as Miranda and Jack, its possible that they're simply using a biotic field to protect them.
With Kasumi on the other hand, this could easily be an justified as being an extension of her shields. We see something similar in the prologue when the Normandy has an emergency shield erected around the cockpit to maintain atmosphere, while Joker's helmet has a visor uses a shield instead of glass.
WorldGalaxy of Badass: Humanity discovers the Charon Relay and zips out to meet a galaxy crawling with raptor-like Space Romans with a fleet whose capital ships can shoot off Hiroshima-level railguns, ninja amphibians who make the deadliest viruses known to the galaxy, Blue-skinned space babes who can kill you... with their MINDS, immune-deprived mechanics who can wipe out a ship with a couple key presses, landshark master warriors who are merely the decayed remnants of the most powerful horde in galactic history, thresher maws, and oh yes, Mecha-Cthulhu. They promptly show themselves to be perhaps the most badass thing to hit the galactic scene yet. Yeah, the Mass Effect galaxy is a constant, ongoing Ultimate Showdown of Ultimate Destiny.
Not to mention EVERY MAIN CHARACTER IN THE SERIES, especially Commander Shepard.
Galaxy of Woobie: Dear lord, everyone in the series, from the ultimate Badass that is Commander Shepard, to the squadmembers, all the way down to the minor bit-characters.
You No Take Candle: How Vorcha speak. They talk no definitive article. Growl lots, too. RaaaAAAAAAAAAAAgh!
Averted/Subverted/something in 3, where some vorcha are shown using correct grammar.
