One of the best games ever made. Its' lack of difficulty and its' short length are definite flaws, though.
The graphics in this game are phenomenal. They are sharp, detailed and perfectly convey the world of Zebes. Each area has its own distinct look and enemies that perfectly complement everything else in the game. Super Metroid is basically Aliens the game (in terms of atmosphere). The intro sequence is especially great in establishing the mood of the game (the start menu and the intro portion) as a dark and lonely one. There has never been a game that has captured the correct atmosphere so well in a 2D game (although A Link to the Past is probably on par).
The gameplay itself is incredibly easy to get into. Samus has a variety of moves including jumping, jumping off walls (a useful tool for reaching hidden items), running, turning into a morph ball (and then setting a bomb or power bomb), swinging on an electric grappling hook, shooting a variety of beams, shooting missiles, running incredibly fast/jumping incredibly high, and the infamous screw attack (jump attack). Each one is easy to use and master, and they are all vital in completing your mission. There are tons of secret areas to explore and hidden powerups to acquire, but even with this in mind you can probably beat the game in around 3 hours. The neat thing about the wall-jumping ability is that can you access later parts of the game with it earlier on. You aren't supposed to be able to, but just the fact that you CAN if you're clever enough is a very cool secret indeed. It's a relatively easy game that is only "hard" on occasion (some of the bosses like the phantom boss can be annoying but not too too hard) and these mar the experience just a bit.
The story itself is kept very minimal (i.e. there isn't much). Basically the space pirates have stolen the Metroid from the research station and you have to infiltrate their home planet to get it back. It's the same as the first game, and despite the intro and ending sequences there are no other story elements presented in the game. They basically give you very little to go on as an excuse to explore one of the coolest worlds in video games. The characters in this game are classic. You have Samus, of course, who has been graphically enhanced to look like the ultimate badass, you have all the classic bosses like Ridley and Kraid and Mother Brain who look truly menacing and tough (despite lacking dialogue they have strong personalities). And, of course, the enemies, including the famous Metroids, are all pretty memorable and engaging.
The soundtrack is extremely mysterious and foreboding. It's eerie sci-fi stuff that perfectly captures the loneliness that Samus is probably feeling exporing this strange technology-infused-with-organic-life world of Zebes. Every area has a memorable theme, and the sound effects are especially exciting (like Samus' charge beam, the super speed running sound effect and the low energy sound effects). There is nothing you could dislike here.
Metroid (NES) may have been the more challenging and longer game, but Super Metroid improved upon its formula to make it more FUN to play. The fact that it's short, relatively easy, nearly plotless and has a lack of replayability (in terms of multiple endings/big secrets/different ways to beat it) could be seen as "flaws" in the game, but despite these things, however, it is a one-of-a-kind experience that every gamer should partake in. Super Metroid is a flawed masterpiece of a game that deserves its spot as one of the best video games ever made.