Update:
Prime 2:
I just need to beat Prime 2 on Hard and than do a speed-run before I move on, but I have finished my 100% run.
After playing through it again, it is definitely the Twilight Princess of Metroid, if that makes sense. It's got the darkest tone of all the Metroid games and the atmosphere feels oppressive at time. Obviously that fits perfectly with the Ing and Dark Aether.
I do love the game, but I'm not sure if it's my favorite of the series.
Mainly because of the Ing.
Don't get me wrong. I love the concept of the Ing. They're an eldritch race of shapeshifters from a dimension hostile to normal life and are basically living darkness.
But despite being the main threat of the game, and the majority of foes you face... they don't have a strong presence. I know that sounds contradcitory, but let me explain.
The Ing are a faceless evil. Unlike every other faction in the Prime series, there is no lore that covers their objectives or thoughts beyond outside perspectives from the Pirates and Luminoth. In a way, that fits with their darkness-aesthetic and their main tool being possession. They are a living darkness that can wear any face, so the mystery is part of the appeal, but... it diminishes their pressence.
Yes, most bosses in the game are literally Ing Warriors just possessing other creatures or machines, and yes they were on the brink of ultimate victory until Samus arrived at the literal eleventh hour... but there's a disconnect between what we see in-game and what little story we get.
When we start the game going through the destroyed GF base, the storytelling implied by the enivronment is that the Marines were suddenly attacked en mass by Ing possessed creatures and even the marines themselves. Then we actually see the Ing at their home dimension, they immediately pounce on Samus and steal much of her equipment and integrate the upgrades into their own bodies. (Sidenote, this is the best "return to zero" moment in Metroid for me.) Shortly after, from the Galactic Federation ship cutscene, we see an entire army of Ing possessed Splinters attack all the Marines at once, probably at the same time their underground base was attacked.
We are introduced early on to the Ing as a very proactive force that attacks offworlders, and they use their numbers to their advantage to overwhelm who they fight.
...And then from there on, the Ing feel very passive. Too passive. Oh sure, they do send some possessed Pirate Commandos after you, but it feels like after that introduction, Samus is mostly hunting the different Ing Guardians herself in their hiding spots, rather than it being her taking on an entire army.
It feels less like you're actively fighting a militant faction that brought the Luminoth to near extinction but are fighting what remains of them in a post-apocallypse Aether.
The lore builds up the Ing as a Horde that fight with massive numbers, eat their dead, and send their weakest younglings in first to soften the enemy. The gameplay never really gives this sense of scale. If there were a few places in the game where you had to fight swarms of Ing warriors, this would help, but the most Ing you ever fight at once is like four or five.
They do a good job of doing some characterizing with Dark Samus in this game, all via her silent actions in cutscenes and such... but the Ing on the other hand after the start of the game lack that, and it hurts them as the antagonists. They even get fully sidelined at the end by Dark Samus taking over as final boss.
Which okay, Dark Samus is the big bad in Prime 3, but... man, I wish the Ing just had more gravitas.
Maybe that could have been fixed by having the Emperor Ing possessing a Luminoth Warrior and have it be more present throughout the game actively taunting her? This game was the first one with active dialogue in a Metroid game, from various Luminoth holograms and U-Mos speaking directly to Samus. Playing more with that from the villain side of things may have balanced it out, and give the Emperor Ing more of a direct presence than merely it being a penultimate boss without build-up.
They're a cool concept, but they just feel too empty as an enemy.
Prime 3:
Doing the final upgrade round-up before I finish the game.
And... for some reason, I always thought the Energy Cells were optional! I thought the whole point of Valhalla was that it was a treasure trove of upgrades and not a mandatory part of the game. Color me surprised when by the end I get the Leviathan Battleship control code. Clearly, they're Prime 3's version of the Artifacts and Sky Temple Keyes.
I have no idea how I came to that conclusion when I was younger. It also means all the "bonus locations" and such I thought were cool are just normal parts of the game.
It's kind of embarrasing really!
Beyond that, Phazon Metroids have gone from the most annoying Metroid to fight to the easiest. Nova Beam + X-Ray Visor means I can just one tap them now. Even their cool Metroid Hatcher mini-bosses go down in one hit.
With the Nova Beam, Phazon has just made the Metroids weaker.
