With SA-X and Dark Samus, so we really need another "rival" type enemy for Samus? Doesn't help that Sylux is incredibly boring and Corruption did the other Bounty Hunters thing better.
Yeah, enough. I hated the "Dark Samus" focus in Prime 2 and 3, especially since that entity is actually the titular character,
Metroid Prime. Having it be a Samus wannabe was just dumb (although I did chuckle at the Space Pirate scans where they're like "OMG now there are 2 of them!).
On the other hand: whatever. Prime 3 had the other bounty hunters, and though they at least weren't bad Samus rip-offs, they were still pretty lame. The game was fantastic anyway, so if that's what it takes to get another good Metroid game, so be it.
Edit: oh, and if Nintendo announces a new "real" Metroid game, then I'll go ahead and buy the spin-off, just like I've done in the past with Hunters and Pinball. But I'm not buying a spin-off when there's not a main game that it was spun off from.