FanficRecs Well, It's Not Other M...
This is a re-telling of Metroid: Fusion, though it goes into a full-on rewrite. It embellishes pretty much everything from the original. The GF has become cartoonishly evil in this version. There's a lot more interplay between Samus and Adam.
On the downside, there's very little sense of atmosphere. Very little seems creepy or tense. Even SA-X encounters aren't that threatening (possibly because it talks. Yes, really). Indeed, the story is very light on descriptions of environments at all, preferring to say "looks like Brinstar" to actually describing Brinstar.
There were a few good elements. For example, the fic gives us the sense of what it's like to wake up and find out you're part-Metroid (though giving her talons on her hand was excessive). And Samus reacts rather interestingly to this.
To me, the biggest failure is Samus's personality and character. She comes across as a typical 80's action hero. She quips. She drinks. She bucks authority. She swears at the drop of a hat. She has a no-nonsense, by-the-books "sergeant" who's in charge of the mission. She even has a plucky sidekick with whom they banter and swap insults.
This even conflicts with her backstory. The fic talks about her being raised by Chozo, but you wouldn't tell that based on how she acts or speaks. She uses all kinds of human colloquialisms and such.
While this is rather personal, I've always felt that Samus is the kind of person who only speaks if she has something to say.
Oh, and then there's the part where she absorbs Ridley's brain. Yes, really. For about half the fic, she has Ridley in her head, talking to her. And even better: they become friends (grudgingly). This fic apparently doesn't include the comic, where Ridley murders her mother right in front of her just for shits and giggles. Here, Ridley is all about a good fight.
Oh, and for the ending (spoiler alert). Samus invades the GF homeworld. Yes, really, she causes the death of what has to be millions of beings. All just to bring down a few guys in the government.
Other M trigger warning: Samus BSODs in this fic. Twice. The first time, it's when she sees SA-X on a monitor. But this BSOD sends her into kill-everything mode for a few hours. The other time, it's when she absorbs the memories of a scientist through absorbing a Core-X. So they're justified.
FanficRecs One of the Best Metroid Fics on the Internet — Though Not Remotely Canon Compliant
This fic is written exceptionally well — professional quality, even. Magus 523's novelizations tend to play fast and loose with their series' respective canons, so it's best to consider this story and its prequel, Metroid III: Return to Zebes as though they were their own entirely separate continuity.
Among certain trigger warnings would be that Space Pirates have a lot more individualism than they do in canon, certain bosses and even mob enemies are given sentience upgrades, and Samus is relatively talkative.
Magus 523 writes Samus as gritty and jaded with no love for the Federation, or even society in general. She's not a silent hero in this fic by any stretch. Quite honestly though, one of the best parts about these two fics is the characterization. There are OCs, but the ones that aren't good are still entertaining to read, and the portrayal of Ridley as sneering, sarcastic and manipulative is a little over the top at times, but they also make him likeable. A sympathetic Ridley is probably not for everyone, but I'd recommend giving it a chance. It's very amusing seeing him cackling as he watches Draygon being killed (there's a kind of rivalry between a 'Ridley and Kraid' faction and a 'Draygon and Phantoon' faction. Return to Zebes was written well before Other M came out and the extent to which Phantoon is actually an eldritch horror was revealed, so it ('he' in the fic) has gotten a bit of a downgrade here.
Samus' relationship with Ridley is akin to two rivals who love to hate each other, and it makes for fairly good on-screen chemistry between them, though not in a romantic way by any stretch of the imagination, thank god. More in the sense of them having fought each other enough to have a rapport. This Ridley's less a murderer so much as he is a fighting-addict.
Quite honestly, these stories don't have an atmosphere of complete isolation so much as they do one of loneliness, often of Samus' own making, but it works for them.
The verdict for these fics is that you should give them a chance. If you're among those of us who forgave Nintendo for Other M, or at least weren't one of the people who turned on the character they claimed to love at the first opportunity for the crime of not being tailored to their interpretation of her, you'll like this fanfic. If you're still aggravated by Other M, or actively avoid looking at anything it did right, I'd advise you to avoid this fic.