It it the first Metroid Game I've ever played. I remember reading glowing reviews and I remember the first time I tried to play Super Metroid.
Am I the only one who did not understand the game at first contact? I think that I am not. That's because Metroid will not show its uniqueness during first minutes of play. To actually feel the mood you have to play for a few hours at least. Only then you will learn that there are no "levels" in the game because the whole world is one big level for you to explore. It is the same feeling as playing any Zelda game - you explore the small area and find some spots that cannot be passed. Then you find some additional equipment that allows you to gain access to new areas.
That's why Super Metroid is not a shooter in my opinion. I think that it is an adventure game that only introduces some shooting elements.
And again - as in Zelda - from time to time you have to fight some bosses. At first glance they look unbeatable but you just have to find a weak spot and make use of it. Usually after a boss fight you gain a new, important piece of equipment.
The graphics and music are first class. You'll often feel small and alone in a hostile environment, having only few life points left and figthing your way to a save point. And then, suddenly you'll start to recognize some places you visit often and feel like home there. To me the whole game area is one big home. That's what a Metroid-mood is!
Even though the game is almost 10 years old, it is still worth of playing. It is in my personal top 5 games list beaten only by Zeldas and the new king - Metroid Prime.