Got potential, but needs a bit more work
Hmm, where to start eh? Well, It is a sprite movie, which (even though I like 'em) need more work than this, but I can see that you're still somewhat beginning, so I'll leave it at that.
Story, there was none. Samus goes of to some random planet, kills a Metroid on steroids and gives us a nice Playboy pose, good enough for the useless fanboys, but not for me. Try working out a bit more on the real evolution and Phazon mutation thing, it is an interesting concept (perhaps mutated forms of the Metroid adult, you know, Alpha, Zeta Omega and such, from Metroid II). Experiment a little, you know.
Graphics, they are almost up to par. One little hint though, don't use sprites and then make self-drawn backgrounds, it looks amateur. Rip backgrounds from games, gives it a more generic feel. I see someone has already made the comment of the correct sizes of the sprites, so I'll leave that. Also one more thing. Diversity, in backgrounds as well as in sprites. The "evolution" Metroid you used was just oversized, a simple recolor might have made it a bit more interesting, so try that next time. For the rest, it was OK, your backgrounds and animations looked pretty smooth so.
Sound, hmm nothing exceptionally wrong with that. Just try to use a bit more SFX (sound effects) next time, when Samus shoots and stuff, makes the movie less boring.
In overall, the movie is a 5 out of a possible 10. It needs work, but there is some talent hidden in there. Next movie, just take a bit more time to polish everything up and you'll have yourself a quality sprite movie (which we are somewhat missing thesedays on NG)
~You've been reviewed~