Mass Effect Legendary Edition includes all three games in Shephard's trilogy and most of their DLC—except Pinnacle Station, a skippable add-on for ME1 whose code was corrupted, and stuff for ME3's absent multiplayer. It's a big package with various changes, from 4K textures and upgraded character models (some of them backported from ME3 into its predecessors), to rejigged combat and controls for ME1. But beyond the back-of-the-box features are some smaller changes you might not notice unless someone points them out to you. That someone is me and these are those changes.
This guy is a turian now
Elanos Haliat is a pirate who ambushes you in one of the first game's slightly less tedious side missions. Though he's got a fairly alien-sounding name and refers to humans as "Shepard's kind", he was given a human model in the original version. The Legendary Edition swaps that for the turian model he was presumably always meant to have.
The Earth is the right way round
When you looked at Earth from the moon while bouncing across it in the Mako in ME1, you might have noticed something unusual. You could see North America, but for some reason Florida was on the west coast and California on the east. No amount of rising sea levels can explain that. The Legendary Edition flips it back the right way round, which I guess means canonically the games no longer take place in the mirror universe.
Feros is health-and-safety compliant
There are a couple of places in the Legendary Edition where railings have been added to locations that where it makes sense for railings to be, like the Presidium. Here on the planet Feros, the Prothean Skyway also has a fence along its formerly exposed left side to prevent you from driving the Mako right off it into the abyss.
The rad cyberpunk visor isn't misaligned
The Kuwashii Visor is a helmet piece you can wear in ME2 and ME3. It projects a glowing blue display that gives you +10% headshot damage, even though the circular part of the display—surely the reticule—doesn't actually line up with your eye. It bothered some players enough that the HR armor mod shifted the reticule into place, but the Legendary Edition changes the visor's look completely so it doesn't even have one.
Pluto's had a makeover
Pluto's important in Mass Effect, as its moon Charon turns out to be a frozen mass relay that gives humanity a leg-up beyond the solar system. You can scan Pluto in ME2, where its ruddy appearance was based on images from the Hubble Space Telescope. A few years after ME2's release, in 2015 the space probe New Horizons did a fly-by and gave us even better images of the ice dwarf, which the Legendary Edition seems to have based its new Pluto texture on.
David Archer's eyes are red and terrifying
In the Project Overlord DLC for ME2, you find out that Cerberus created a cybernetic synthesis of man and machine to control the geth. As usual, things went wrong and the geth became violent. Eventually you learn the lead scientist in charge of the project put his own autistic brother David into a horrifying Clockwork Orange machine to fuse him with a VI, and that's how he's been controlling the machines. David looks more cyborg in the Legendary Edition, with bright red eyes. Of course if you're playing Renegade you probably do too.
Illium's got weather
While the additional snow in Noveria in ME1 is hard to miss, making the approach to Peak 15 seem more like a blizzard, the asari world of Illium also has more noticeable weather. In both cases the main impact is that it makes the skyline harder to see, as the outdoor area of Illium is now covered in foggy cloud.
Jack has seen some shit
Between ME2 and ME3, assuming she survives the suicide mission because you remembered to upgrade the Normandy, Jack grows back some of her hair. While the original version of ME3 gave her a brown wolf tail, in the Legendary Edition she's gone a bit gray. While not the only character to have her hair tweaked in the remaster, this one seems to have flown under the radar while everyone's busy being furious that Kelly Chambers isn't a redhead in ME2 any more.