So sorry all you Halo-Loving poser Metroid fans, but your tears of sadness taste like candy to me.
But seriously, Nintendo/Retro has been saying there wasn't going to be multiplayer in this game for over a year now. This shouldn't surprise anyone even a little.
Just think about it though! Retro has spent the better part of the last three years crafting/refining this game, and likely cramming in more detail, more art, more lighting effects, and more AWESOME into this game, we probably won't see this stuff again until Retro makes another Wii game.
It gives me chills. The good kind.