Snoorlax on 17 June 2017
If you care about the main story i suggest playing in this order.
Metroid: Zero Mission
Metroid II OR wait for the remake Samus Returns (<recommended)
Super Metroid
Metroid: Other M
Metroid Fusion
The Prime games follow their own story and should be played in this order.
Metroid Prime
Metroid Prime: Echoes
Metroid Prime: Hunters
Metroid Prime: Corruption
All these games have their own unique gameplay differences and should really be played by yourself rather than following advise on which game is best in terms of gameplay.
