Ah bugger I forgot to talk about the Platform leading game... yep Halo is THE biggest game on the Xbox 360. I don't think that there is one sigle game that is a Platform leader on Wii, honestly I don't think Nintendo wants it that way as well... why restrict your biggest game to one genre and one game? Yeah there are other big games for 360 but Halo 3 is the biggest, and once its gone there is nothing as big as that any more. Nintendo has spread their 'biggness' around, and while Metroid isn't the platform leader it's the genre leader so yes, I think it's in the same category and league as Halo. I think it is silly for Nintendo to not position this game against Halo head to head, it's why it is strategically releasing a month before Halo, enough time to build up hype and steal some of its thunder if word gets around that this is the new best thing since sliced bread because of the new controls.

 Sorry 'steal' is the wrong word... by steal I mean 'turn' i guess.

Yeah. A lot of people still think Microsoft should have named the Xbox 360: 1) Halo Box 2) FPS Box

It seems possible , specially since the amazing sales Wii is having... I think halo3 wont reach halo2 levels, and that is becuase its a new machine with not nearly as much installed base as when halo2 was released... I think that was the reason that Halo2 sold better than the first one. With metroid prime 3 being in the console with the most userbase in the holiday season and onwards, and showing the capabilities of the system for FPS GAMEPLAY. It really is plausible for Prime3 to get stellar sales, and get a chunk of the FPS pie. Not by any means overtake it, but being competitive.

Metroid will not have a chance to be close to Halo no matter how good it is unless it's multiplayer (which I doubt). Multiplayer games have a lot more sales. I think Nintendo (or third party) will come out with a decent multiplayer FPS, but I don't think it will be Metroid. Assuming Metroid is not multiplayer, I think Nintendo will be (or at least should be) happy with 2Mil.

If Metroid Prime 3 uses the online(without the friendcodes issues) it will have a much bigger impact on Halo 3 sales, wii owners will have their "Halo", with this people who doesnt have a 360 and where waiting for Halo 3, will have 2 options: The Cheap one with better story/single player and online(if it is done right) for $300($250 the console+the game) and the expencive one with good online and not so attractive for story/single player for $510($400 console+Gold account service+the game).

All of this is speculation, but if that is what nintendo is thinking, Metroid Prime 3 will steal A LOT of the Halo 3 success, but not enough to match them. It will be an interesting race

The Metroid Prime games have been about merging shooting elements and adventure game elements in an attempt to create a game which is unique; unlike most FPS the enemies each have distinct weak points which need to be exploited, there is a focus on exploration, puzzles and boss battles. Hypothetically speaking, the games have always had the potential to sell huge quantities.

Both MP1 and MP2 were heavily hurt by the low popularity of the Gamecube but Metroid Prime 2 was released at the worst possible time. Q4 2002 saw the release of Metroid Prime 2 (Gamecube), Halo 2 (XBox), Half Life 2 (PC), Grand Theft Auto: San Andreas (PS2),  World of Warcraft (PC), and the Nintendo DS. To a certain extent I think this is why Nintendo is targeting an August release; it will give Metroid Prime 3 a month (or possibly longer) before the other companies release their major titles this year (GT4, Halo 3, Killzone 2, etc.).

An interesting read from the original Metroid Prime's wikipedia article:
"The game was first announced at 2001 E3 and was revealed shortly after to be played from a first-person perspective. Following the announcement and subsequent release of first screenshots, the nature of the game aroused the ire of fans who perceived it as a disgraceful transition into 3D.[2] In addition, due to frequent layoffs and corporate reorganization at Retro Studios during development, the game was often feverishly considered a debacle throughout gaming related message boards, publications, and magazines until near the point of retail release when various publications claimed it as one of the greatest video games of all time.[3] It was also a commercial success, selling over 1 million units in North America alone. [4]"

I dunno...I just found it interesting that so many people ridiculed the game, though it was because of its 3D nature I'm sure...but the end product was a beautiful masterpiece...and I'm hoping for the same experience again.
A lot of people push MP3 around for its crappy screenshots...but if it controls well, and looks good for a Wii game, I can see this game being amazing.

Sorry, a bit off-topic. 

Great read, Metroid 3 can certainly get at least double the sales of it's two 3d predecessors, but i'm not optimistic enough to say that controls will be enough to reach Halo 3 sales.. that game (Halo 3) doesn't even need to be good, and it'll still get 4mil sales purely because of its fanbase. My idea is that if the Metroid controls are perfect, or near to it, the Halo sales won't drop, but the margin between Halo and Metroid will greatly narrow

I don't think it is a fair comparison. First MP is not even a FPS anyway. Also you are comparing the most popular game on the 360 to a semi popular game for the Wii. I think Brawl vs. Halo would be a better comparison. Also MS has committed themselves to the FPS genre, that is pretty much all they have.