Gamespy today ran an interview with Metroid creator Yoshio Sakamoto in which he talks not only about the upcoming Metroid: Zero Mission (just 7 more days!), but also talks about the series' origin. Not simply a port of the original NES Metroid, Zero Mission is a brand-new adventure:
Samus has new powers, there are new puzzles, there are three difficulty levels to choose from, and the story goes off in totally new directions. Sakamoto even revealed that 25 to 30 percent of the game takes place after the pivotal battle with Mother Brain -- which marked the end of the NES Metroid.
Details I found interesting: Zero Mission will connect with Metroid Fusion in some way; and for a period later in the game in Zero Mission, Samus will operate outside of her armored suit.
I'm looking forward to playing the new Metroid game as soon as it's released next week!