Alright, a quick low-down of what I have played so far of it:
Takes place almost-immediately after Super Metroid in the terms of storyline, it gives a little more insight on events leading to her going from Galactic Federation Army to bounty hunter. The whole "side-scrolling" business of it is not truly a 2-D side-scrolling type of gameplay but you actually can move around in all four directions on the ground and ascending/descending add to the movement to make it a truly six-axis gameplay with the emphasis on action. Now, you have to be able to quickly go from normal mode to Search Mode (using the pointer on the screen to observe and scan) in some cases, but the feel is rather fluid in my opinion.
To the die-hard fans of the series, I'd say you shall not be disappointed with the action and the story. To newcomers, you're in for a real treat.