What is MEtroids story?
Play them, cheater =p
Or maybe GameFAQs has something about it, lemme check...
...well, as I figured, they have an ending FAQ, and I'm sure you can check a FAQ from each game to read the Introduction that's included in the games instruction manual. That'll give you the entire story.
Here's a link to Metroid for NES, which includes the Metroid Endings FAQ.
If you'd like a list of the Metroid games that exist, here:
Metroid - NES
Metroid II: Return of Samus - GameBoy
Metroid III: Super Metroid - SNES
Metroid IV: Metroid Fusion - GBA
Metroid Prime - GCN
Metroid Prime II: Echoes - GCN
Metroid: Zerio Mission - GBA (a remake for the first Metroid, and a kick-ass one at that)
Have fun.