Time for Metroid Prime 2 hype!

Actually, the Space Jump is in Metroid Prime and MP2. It's just a double-jump function. The Screw Attack now carries all of the hovering properties in the 3D series.

The space jump in MP is the same concept as the old metroid games but she doesn't spin, in MP2 she will be spinning(meaning she can use the screw attack as well).

Well, no it's not the same concept. In MP the Space Jump is just a double-jump. One extra jump in midair is all she gets. In the 2D games, the Space Jump is a multi-jump, meaning she can basically hover in the air for an infinite amount of time.

In MP2, the Space Jump functions exactly the same way as in the first MP. It's just a double-jump. When Samus gains access to the Screw Attack, it pulls the camera out into a 3rd person perspective and allows her to multi-jump in a lateral direction only. She can't gain altitude when using the Screw Attack in MP2.

The multi-jump capability is now built into the Screw Attack, not the Space Jump.

Will it have the same harsh timing requirements as the 2D games? You say she can basically hover indefinately, but the correct phrase is she can theoretically hover indefinately, because in fact, it is very difficult to pull off, unless you can find a nice, inert wall to hover beside.

Also, why does there need to be multi-jump for the screw attack? In Metroid II, the screw attack was just as deadly without spacejump; the only real reason the two needed to go together was to escape the un-screw-attackable metroids, speaking of which, will you still be invulnerable while screw-attacking?

As far as I'm aware, yeah, you're still invulnerable. It still requires the timing to pull of the multi-jump as well.

As for why they combined them, it would be pointless to include the Screw Attack into a Metroid Prime game without the multi-jump attached to it. Doing so would create a gameplay mechanic in which the view would pull out into a 3rd-person perspective every time Samus jumps, as opposed to just pulling the view out for when she activates the multi-jump. It would be too disorienting.

Just thinking about it, it seems to me like the game would be better if it was completely third person.

...obviously you've never played Metroid Prime. If you had, you wouldn't have said such a thing.