If memory serves, there were those who were skeptical that Metroid being done in first person would doom it. Whatever new twist they put in Metroid Prime 2, I'm confident that Retro will do it tastefully.
Interesting is the fact that while Nintendo's other franchises have 'families' to them (Mario and Luigi and Co., Link, Zelda, Ganondorf, Various other Races, the Star Fox crew, Kirby and that mouse, etc..) Metroid simply had 2 factions: Samus and the enemy. I would welcome the chance for a 3rd faction, whether be it friendly, neutral or hostile to Samus.
Multiplayer? Its as simple as turning auto aim off, no biggie, just gotta learn to aim.
Perhaps an optional Co-op LAN? That would spice things up if you have the gear.