To me the first Metroid is the best and it’s still playable (I’ve played it quiet a bit on the NES app you get with Nintendo Online). Super Metroid is a superb game by all means, it’s just that the first one is better (to me).
It comes down to the ”no hand holding” approach. No minimap, no markers (for items or objectives), you are just dumped into the world and need to find your way. Playing it today I can finish it fairly quick because I roughly know where I need to go to. But for a first playtrough you get some serious time out of it (unless you use a guide or look things up online).
While Metroid Prime is an excellent series (if you exclude the DS title) I don’t really consider them as Metroid, except in name. The 3D environment messes up the Metroid feeling.