fooflexible on 21 February 2007
shams said: There is a 100% chance that Metroid will launch this year - absolutely guaranteed.
Here's a link to a story about Metroid's uncertainty:
Nintendo President Dodges Question about Metroid release date
Finishes by saying: "...we shouldn't be too surprised if we heard it's due for early 2008."
Nintendo knows that this is the game that has to prove Wii is the ideal FPS system, so it has to be perfect, plus I personally think there going to try and beef up their online support with this title. Both elements could have set the title back a bit.
I was just reading an old interview and it mentions an interesting point, one of the reasons why Mario and Metroid were originally slated for early 2007 were to prove Nintendo would have a steady stream of games launched early in the Wii's life. That was before there hit launch, and many 3rd parites pledged new support. With big sales they no longer had to rush these games to the market, they could tweak them to perfection and use the them too boost new horizons for their system down the road. In turn they must have used titles like Super Paper Mario to fill the void.