I played the original, Super Metroid and Metroid Fusion. Never could really get into the original, I'm afraid, it's just too 'basic'. Should play Zero Mission, but I don't really want to on Virtual Console, I want a good boxed GBA copy instead. Which sadly is hard to find for a decent price.
Super Metroid and Fusion are both amazing though, and I have both in Smeags's end of the year top 50 thread. I rate Fusion just a bit higher though, and as such is my favorite Metroid game, because of it's story. While the non-linearity of Super Metroid is great, I like the structuring of Fusion better.