I actually have almost as much of a problem with the gameplay as with the story.

In addition to the issues you mentioned, it has tons of flaws in my view; the fixed camera that often has you unable to see ahead of you when moving towards the screen, the stupid health system, (they should have just used powerups like prior games) the sections where you are forced to walk slowly from A to B with nothing happening, the inherent problems of using D-Pad movement in 3D space, the inability to move in first person view but being forced into it to use missiles, the list goes on and on.

XCX is a good start, but its just one game; they need more like it.

 It proves that Nintendo is still completely capable (and certainly has the "guts") to fund and making grim, beautiful, ambitious games. Nintendo's never really made many of these types of games. Even Metroid Prime, I wouldn't really call "grim" or "ambitious". Where it excels is level design and atmosphere.

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A Metroid reboot for today's market would have to be significantly darker and more visually polished than XCX. It would need high end graphics, (or at least, as high end as the platform allows for) and a more serious tone.

Prime is considerably more sombre than XCX; there is no comic relief, no bubbly characters, no cheesy moments.

I'll gladly buy one in the release date as long as they made a good real Metroid. It's hard to do so when they keep releasing shit nobody asked for.

Prime is grim, dark and ambitious.

If Nintendo really have the guts, the would have made a Metroid game already, dark Paper Mario, a more Galaxy style 3D Mario, Zelda would have a more similar TP art style.

If by "dark" you mean "parts of the game are pretty darn dark"  than I agree. Otherwise, the game doesn't really fit any of those criteria.

I'll admit the opening of the game, on the half-destroyed pirate vessel, is a little grim. But pretty much all of the violence and unfortunate happenings occur against these ugly looking enemy creatures. I wouldn't call that grim.

The game also isn't especially ambitious in scope or technology. Where the game excels, is how it translates the 2D Metroid formula into 3D. The game has AMAZING design, but as far as the scope or technology goes Metroid Prime was fairly modest in 2002. Ambition isn't what made the game great.

I also don't see how making a darker "Paper Mario" would solve people's problems with Sticker Star's game design. TP's style is pretty widely considered to be kind of ugly by today's standards, especially in comparison to the more cartoony look of its predecessor. Making a sequel to Super Mario Galaxy doesn't require "guts" when the template has already been utilized and proven twice on ancient hardware. Nintendo probably hasn't made another Metroid because Other-M has been reviled by a lot of people, and Retro's been busy with Donkey Kong Country Returns (the first of which sold way more than any Metroid title).

Not really. A Metroid reboot need be no darker than Prime was, which wasn't especially "dark" itself. For an open world game on the Wii U, XCX has damn good visuals, and it has plenty of serious moments. A modern Metroid "reboot" wouldn't need a grim-dark story with Samus brooding all the time and no light moments. This isn't the 90s. If anything needs to change, it's the game design. A new Metroid ought to be bigger, less linear, more open. Personally, I've always thought Metroid would work extremely well with an open world space-sim overworld. Flying around the galaxy and docking with randomly generated abandoned ships and space stations floating between planets that make up the core game's content. Maybe land on asteroids and explore abandoned mining facilities, attacking pirate moonbases for bounty, etc. In addition to the usual first person exploration and puzzle solving of the Prime games, of course. Ambitious, but totally doable by today's Nintendo.

XCX has comic relief, but then, it's also about the near extinction of humanity. The whole story is about as grim as you can get without making something that's just dull and depressing. While I haven't beaten it yet, I expect we win.

I wouldn't know about Prime being "sombre". The game barely has any story to speak of. It has plenty of logs from the pirates, but those tend to be written in a dull, scientific tone that add flavor and atmosphere to the world. But there's hardly enough there to really call the game conisderably more "sombre" than XCX. The dungeons are dark and you spend the entire game by yourself, but that's hardly "somber".

XCX was full of both intentionally and unintentionally cheesy moments that Prime simply doesn't have.

Prime's darkness comes from everything from its sound design to its scan logs, (which include gruesome clinical descriptions of how Space Pirate corpses were killed) to circumstances, (gunning down wounded and dying Pirates aboard the Orpheon) to its focus on solitary confinement. Nothing in the game ever breaks or lightens this mood.

"This isn't the 90s" actually sums up why it should be dark; audiences these days prefer games to be serious.

And while XCX looks about as good as is realistically feasible given the hardware its on and the gargantuan scale and seamless nature of its world, the latter necessitates some compromises, such as simplistic character models. A modern Metroid would need to be more visually polished.

Prime doesn't have those moments because it doesn't really have a story. It has atmosphere and a barebones plot. And through out XCX you're constantly hearing about people dying, about how dangerous and brutal the world is, and you're fighting an alien race that has not only blown up your entire planet but is dead set on killing the rest of you. Stories like these NEED moments of levity.

"This pirate was killed by a plasma blast to the sternum" doesn't really add to the darkness. Gunning down wounded enemy aliens isn't especially dark. Neither is reading reports about status reports from pirates to their commanders. Your killing enemies you have no inclination to feel sorry for anyway. It's not like your seeing dozens of civilians die. It's not like your making hard moral choices. Your killing enemies and reading logs.

What Prime has is a great atmosphere that's good engrossing you in its world. But that's not the same as making a game with a super serious, grimdark storyline. It's easy to not have any comic relief when you have no plot to house it.

Even friggin Witcher, Mass Effect, and Elder Scrolls have moments of levity and humor. That doesn't take away from the fact that the subject matter and happenings in these games can still be quite dark.

I bring up the 90s because media from that era is known for being "grim dark" for the sake of it. We've grown out of that nonsense.

Sometimes in Zelda it's not really gibberish:

Midna's Voice Clips - Unscrambled

Fi's voice also sounds like scrambled Japanese

Zelda Skyward Sword - Fi Voice Clips Reversed

Prime does have a story. It's just not spoonfed to the player in elaborate cutscenes. 

And it adds immensely to the mood to read that the corpses I have come across were killed recently and drained of their blood, (this evokes dread) or that the Pirates I come across have broken legs and can't flee, or cannot aim at me properly because they have suffered brain damage. Even an alien foe can illicit mixed feelings when I am essentially executing wounded soldiers.

XCX has its dark moments, but its cheesier scenes prevent it from having the kind of tonal consistency a modern Metroid would need.

And I am not talking about being "grim dark for the sake of it" (Which I personally think is a rather baseless argument. Can you give examples?) but grim/dark because it suits the source material. Metroid is an intrinsically dark series. Even before Prime, Super Metroid had human corpses on its title screen. Given that this style of game has risen enormously in popularity over the last decade, and is sorely lacking from Nintendo's catalogue, it makes both commercial and artistic sense to make a Metroid reboot a thoroughly dark and serious affair.

Prime has a plot and atmosphere, but its story is barebones.

Hearing about soldiers getting massacred by local packs of alien predators and powerful tyrants can evoke its own bit of "dread" (though not on the level of the few moments you've referenced in Prime) but nevertheless I wouldn't equate that to "grim darkness". And I think it's also telling that a lot of the stuff your mentioning is mostly only seen in the opening area of the game. Most of Prime isn't even this dark.

Prime can have tonal consistency because it has very little story with no characterization. You play a blank slate in a world empty of characters. You'll be hard pressed to find a quality RPG that doesn't have some comic relief in it.

In any case, as far as tonal consistency and a dark atmosphere, what you highlight in Prime isn't just something that modern Nintendo doesn't do. Nintendo in general has rarely ever gone in this direction, and the few times it has has been in games that are hardly "consistently dark".

There is nothing about Metroid Prime that modern Nintendo wouldn't have the "guts" to do. Dark games in general have always been a rarity for Nintendo.

I do agree with you on one thing: I do think it would be good for Nintendo to diversify it's library with more "mature" games. Bayonetta 2 and Xenoblade Chonicles X are a nice start, but these types of games should be more than just an occasional occurrence as they long have been with Nintendo.