Not only is Super Mario World the best game of the Mario series, it's one of the best games of all time.
Now that we've gone through that this game is the definition of "masterpiece," let's move on to the the Big Five, shall we:
Gameplay/Mechanics:
Anybody who truly considers themselves a gamer should know what Mario's formula is. In essence, run, hop, and hit blocks until you get to the end of the level. That's over with now? Good.
Super Mario World (SMW) introduced a new mechanic that many enjoyed using on poor, hapless enemies, the SPIN JUMP!!! Not only was this great for dealing with Bowser's evil minions, but they were also helpful in destroying many of the supposedly indestructible blocks. Speaking of which, SMW introduced a host of new block types, many of which actually required some thinking to get through. From blocks that would disappear, only to reappear again, to trampoline-like blocks that could only be accessed by riding Yoshi, SMW's gaggle of new blocks provided a challenge to the most seasoned Mario vets. Another new addition was Yoshi, the talking dinosaur with a huger appetite (more on this in the Characters section,) who actually proved to be quite a help on your quest, as well as being a useful powerup. Another new power was Mario's Cape, which was basically the Tanooki Suit in Super Mario Bros 3, but looked cooler and still proves to be a deadly weapon in Smash Bros.
Graphics/Art Style:
For it's time, the game's graphics were beautiful. The bright colors and great scenery really set the overarching tone for the game, and, for the time, there was a lot going on in some instances. Compared to SMB3, this game blew peoples minds. Mario had pant pockets. PANT POCKETS. That was a huge deal back then.
As aforementioned, the game's art direction was really bright and vibrant, something that enticed young gamers and charmed adults. Even when you were in the mansion of ghosts and everything was supposedly scary, the game still gave off a certain happy vibe. And not only that, but Mario's mustache looked grander, which should be a plus in anyone's book.
Music/Sound:
The music in this game is often considered to be some of the best in the series, despite most of the tunes being remixes, and once you listen, it's not hard to understand why. Rhythmic tunes and upbeat mixes give a great feeling as you jaunt through the world, flattening Goombas back into pancakes and hoping through blocks. The fact that Koji Kondo composed all of it by himself using only an electric keyboard is pretty astounding as well, but given that it is KK we're talking about here, it's not entirely unbelievable.
The sounds of this game are also nice, but are a simple staple of the Mario series. The "dings" and "beeps" that you here when you collect coins and squash enemies are still there to lift you up, but there's nothing especially new here.
Storyline/Characters :
Well, this is a traditional Mario game, so expecting this game to have an epic plot in the vein of an RPG is pure lunacy. That said, though, the game's story isn't even original for a Mario game, it just sticks with the "save the princess" vibe, which I am more than happy with. In fact, if the game had a great story, hardcore gamers would reject it as "not Mario enough." That's just how well-established this hop-n'-bop game is.
Similarly, the characters haven't changed much either. Toadstool is still the damsel in distress, Bowser is still the evil overlord, Luigi is still a simple palette-swap, and Mario is still the go-to plumber we've all loved. However, this game marked the entrance of the talking green/red/yellow/blue dinosaur Yoshi, who was a crazy-helpful powerup as well as a fan-favorite. Yoshi could swallow enemies and spit 'em back out, Kirby style, or swallow apples and use them to pick off enemies. You also moved faster and jumped a little higher with the plucky dinosaur in tow.
Replay/Multiplayer:
The game's general replay value solely depended on how dedicated you were to collecting all the coins on each level, to boast to your friends how awesome your skills were. Other than that, the levels are still fun when replayed, but the same feeling of newness that makes every level in SMW different is lost. You expect everything. However, the levels are fun, even when replayed, in multiplayer mode, for reasons that baffle mortal men.
The games multiplayer is where you truly put your skills to the test. With one person as Mario and the other as Luigi, you individually approach different levels, switching turns every time a person dies or completes a level. While this may seem standard, and it is, there is a certain difference in this game. You couldn't lose, because if you did, not only would you be taunted mercilessly by your "buddy", but you would lose a life, and eventually die. Now, you could NOT, under any circumstances, get a Game Over with your friend right beside you. That was like proving their superiority. It was with this knowledge that you would perform exceptionally well, desperate not to die, and grow your skills as a gamer.
The bottom line is, that there is no point in me reviewing this game. Any serious gamer has played and loves this title, and if you haven't, well, why aren't you playing it now?