In ways Metroid is supposed to be a counter for Halo, but only as far as it is supposed to appeal to a very similar demographic (western male core-gamers) and it is not supposed to be a very similar game. The gameplay mechanics of Metroid are a combination of First Person Shooter elements (like Halo) and Adventure elements (like Zelda) and unlike most games Metroid is meant to be a much more introverted/isolated self-motivated game.
As far as countering Microsoft in USA, I'm not sure any game in particular is really all that important for Nintendo. In the first 6 months of 2007 the Wii has outsold the XBox 360 by (on average) 35,000 units per week and almost a million units total. Without considering holiday sales boosts, if sales continue at this pace the Wii will outsell the XBox 360 in North America sometime in late 2008; the Holiday season adds the potential for the Wii to sell 1 to 2 Million units more than the XBox 360 in 2 months (an unlikely situation but it is a possibility) which would mean that the Wii could pass the XBox 360 in early 2008.
Personally, I would say the real question is whether Grand Theft Auto 4 and Halo will provide enough of a boost for Microsoft to maintain their lead?
