The second metroid was much more linear then the first one, only thing was since it was still in it's infancy as a series, it's not well defined. No map may get you confused unless, you know that you have to keep going down in the game (theoretically). Other then that, it's a fun game to play and the various forms of metroids are pretty cool.

Fusion, was technically my reintroduction to the series, since I never really got to play Super Metroid, but it really is downgraded to easy because I want to say they weren't really sure how the consumers of today would feel with a hardcore Nostalgic Metroid game. But I liked it, it was fun and had a nice little plot twist.

I'd agree with starting with Zero Mission then Super Metroid. Only issue is, once you skip up to Super Metroid, you kind of are obligated to play the second metroid since it's a direct sequel, not like Zelda, where you can start at anyone of the games and be alright. But if you don't play the second one, then no harm no foul since Super Metroid's introduction scene is one that explains a lot more then some other games.