Super Mario Bros. 3 is the third (or perhaps technically fourth) Super Mario title, originally released for the NES. Some people have revered it as the greatest game ever for that system, released in 1990.
This may well be because this is such a revolution / step-up in the gaming world, not only for the Mario series, but for the entire world of gaming as a whole. The game follows the standard storyline: Princess Toadstool is kidnapped, and Mario / Luigi is drafted to go save her. However, the flow of the game's worlds is actually not nearly as predictable as the storyline, and that's what makes it so incredible. This is because not every world ends with a castle; there will be times when you have to defeat a Koopa on an airship in order to save the world's transformed ruler. While this doesn't affect the game's nature very much, it was an interesting twist on an old story.
The first big change would be the item-retention option. This allows you to hold in check any items that you pick up from Toad Houses around the map, as well as others you earn for beating castles, etc. This is a really useful option because it allows you to enter a level prepared for what is coming, as opposed to the original Super Mario Bros. where all you had access to all the power-ups within the levels.
Now let's discuss the items themselves: there are so many and varied items in this game that it will make your eyes pop. It has the standard Super Mushroom, Fire Flower, Starman, and 1-Up, but it also features a huge amount of additions; these include the Tanooki Suit, the Super Leaf, the P-Wing, the Kuribo Boot, the Frog Suit, the Whistle, the Squirrel Suit, the Anchor, the Hammer Suit, the Music Box, and the Cloud. It's almost too many to list! I'm already tired.
This enormous amount of items combined with the ability to instantly arm yourself makes this a fun and exciting gaming experience right off the bat. As a person who hates going into things unprepared and defenseless, I love the option you have of equipping yourself with something that will help you to survive.
Now let's talk about the worlds. This is an incredible improvement in terms of worlds, as it is the first to allow you to travel across a world map, where you can revisit levels, do puzzles, visit Toad Houses, confront wandering enemies, and travel through pipes. This puts a tactical spin on making your way through the game, which is incredibly fun and engaging.
The game has also improved upon the issue of lives, as 1-Ups are more and shorter between, plus whenever you get Game Over, you only start back at the beginning of the world you're in, as opposed to the beginning of the whole game. You can also play through mini-games and earn cards (as you play through the levels) to earn varying numbers of 1-Ups. This made it waaaay easier to progress through the game and experience what it has to offer, which I loved because I continue to be frustrated by my ability to only play through the first few levels in a Mario title for the lack of ability to get past only one in particular.
However, the final and biggest improvement of this entire game is the new world types.
In contrast to the original game, which only had Ground, Underwater, Underground, and Castle levels, this game has Desert, Ice, Cloud, Airship, Giant, and Pipe worlds, in addition to the previous four and world 9, which allows travel between worlds. This was the best aspect of the game, because it made for very varied gameplay and fun experiences that made you want to come back over and over again just for the sheer fun of playing. For example, I love playing through both the Desert and Giant Worlds, plus the Pipe world is pretty fun as well.
This may very well be the greatest game ever made for both the NES and SNES. It's fun, replayable, diverse, and enjoyably challenging, and it will probably remain the greatest Mario title for many years to come. Now matter how you do it, you should absolutely, without question buy this game now.