These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Ridley, whose theme in this game is memorable enough that it's reused as his theme throughout the series from this point on. (The theme wasn't exclusively Ridley's in this game, but it would be used solely as his theme in future entries).
Even Better Sequel: While the previous two games were good, Super Metroid is considered the game that defined the genre.
Good Bad Bugs: Quite a few of them exist. Most of them can be used for Sequence Breaking, like a bug that lets you open certain Super Missile doors from the wrong side, but one that involves equipping both the Spazer and Plasma Beams lets you travel back in time, resetting all the game's events and collectibles while leaving Samus's inventory (minus missiles) intact.
Using the Spazer/Plasma combo glitch can lead to one of three unintentional weapons.
Combining all the beams but Wave create the Space-Time Beam; with it, Samus can reset time, beginning the game again with everything but her missiles intact.
The Murder Beam (all beams) continually damages bosses to the left of the shot, making bosses that are generally to the left of you (Ridley and Mother Brain) near enough a Curb-Stomp Battle to Samus.
The Chainsaw Beam, the least useful of the three, does no damage to enemies, but breaks blocks insanely fast, making it more of a Utility Weapon than an actual weapon.
Growing the Beard: The first two Metroid games were fine games but had very noticeable flaws. Super Metroid improved everything. It had better gameplay, better bosses (including one of the most highly regarded Final Bosses of all time) and masterfully told minimalist story. It also practically defined the Metroidvania genre.
Magnum Opus: Generally considered as the best installment in the franchise.
Seinfeld Is Unfunny: Modern gamers will find the game to be pretty good, but they will be scratching their heads wondering why everyone acts like it completely revolutionized action-adventures games. The open world exploration may seem kinda basic and slow nowadays, but back in 1994, no game was as huge as this (it was the largest game released at that point).
Tear Jerker: The Super Metroid's Heroic Sacrifice, done completely without dialogue, is probably the saddest moment in the entire series.
Tough Act to Follow: The biggest reason there was not a Metroid game for the Nintendo 64, was because nobody could figure out how to make a worthy successor to Super Metroid. Thankfully, when Metroid Prime was released, it mostly avoided this.