Let's start right with the star of Super Metroid.  No, not heroine Samus Aran, but the alien parasite bugger itself.  After seeing different variations of Metroid in the previous title, Metroid II: Return of Samus, it seems a like a step back to encounter a regular plain Metroid exclusively here, but these creatures are far more terrifying and intimidating than their further developed counterparts.  Note the veins and membranes clearly visible.  Stare at it long enough and you can almost hear its chilling screech.

 
Mother Brain, seen here in her tank as a stationary target.  Never you mind what happens when she breaks free.  Later Metroid games would set up the backstory of Samus's most memorable nemesis has being a Federation Aurora Unit stolen by Space Pirates for their own nefarious plans, etc. etc. etc., but in 1994 all we knew was this Mother Brain controlled the pirates' plans and therefore must be eliminated.  Somehow, knowing less about her made her more threatening. 

 
One of Mother Brain's loyal subordinates (as far as Super Metroid is concerned), Ridley has a knack for turning up again and again despite supposedly being dead.  This artwork manages to make the leader of the Space Pirates look less threatening, surprisingly.  A mere image cannot depict his telescopic tail or fire-breathing talent, nor are his deadly claws all that evident here (instead, they merely look painfully sharp).

 
Unlike Ridley, Kraid actually seems to be dead and gone after his defeat in Super Metroid.  Despite plans to bring him back for other Metroid titles, his appearance here is his last in the series timeline.  That's a shame, but at least he went out with a bang in this larger form compared to his previous appearance in the original Metroid.  Jamming Super Missiles down his immense gullet is one of the high points of the game.  This image doesn't do his large size justice.

 
The Spore Spawn turns up as a mini-boss in the Brinstar region, although seen here isolated from its habitat, it doesn't look all that threatening.  Taken in context, however, it's a massive beast of a plant.  Those red nodules look suspiciously like a weak point.  It's almost as if the spawn is one of the first bosses Samus encounters once the learning curve portion of the game is over. 

 
Phantoon!  Within the Wrecked Ship waits this ghostly creature from beyond the moon.  Figurative moon, mind you; I'm not sure if Zebes has a natural satellite.  But I digress... a look at this Phantoon artwork allows us to get a solid look at him without all of that phasing in and out of normal space business.  The teeth around the eye (or is it the eye inside the mouth?) are a nice (if terrifying) touch.

 
Admit it: when you see the demon shrimp Draygon, all you want to do is pepper that soft underbelly with missiles.  He seems like a creature designed to take a pummeling from underneath.  Yes, it's also possible to electrocute him with careful use of Samus's grappling beam, but that takes all the fun out of blasting a hole in his gut. 

 
Based on this pose, this Torizo would like to clarify a point.  Can't you almost hear him saying, "Um, excuse me..."?

  
Samus famous gunship with the lady herself standing on top is a famous image, although assuming the scale here is accurate, that ship must be very cramped inside.

 
Here Samus dahses into an oddly out of proportion save station.  Her tinted visor is very stylish, don't you think?

 
At last we get a look at the face behind the helmet as Samus Aran flees an explosion in what has to be a physically painful pose without the protection offered by said helmet.  Samus was going through her purple-haired phase during this time following on from her green-haired period and just prior to returning to her now-traditional blond.  Still, no matter how awkwardly she's depicted, she's always the go-to bounty hunter when parasites and pirates cause trouble.