Whoo! I LOVE THIS GAME!!! And the screaming in pain involved.
Okay, about the gameplay. THIS is where the game really shines. This isn't your grandma's generic platformer, no-sirree.
The world system is simply awesome. It allows you to choose between worlds, challenge hammer bros and company, and even play a remake of Mario Bros by pressing A when both players are on the same square! Toad houses allow you to gain items, coins, and lives. The gameplay itself is seriously open. With more powerups than any other Mario game, it's extremely fun not even knowing what powerup you'll get next. The amount of secrets is amazing. Things like giant boxes with some of the best powerups, new rooms with lives, or maybe even a large room of coins, you never know what you'll find in this treasure-chest of a game. Some levels are quite easy, while some are insanely hard and make you want to cry to your momma because you die by bouncing off a wall. All of the levels are fun however. And one last comment of the gameplay... Boom boom is absolutely pathetic.
Okay, now about the graphics. These graphics are cool. The amount of sprites some enemies have is awesome. Although the graphics are standard for the NES, they're still quite good.
Okay, now for the sound. A lot of the music is memorable, and much of the sounds are classic, so most of the sounds are cool.
If you really want to play this game over and over, please do it in 2 player. It makes it more fun.