This game didn't deserve the Super Mario Bros name. It runs completely out of the Mario world and has ugly visuals.
You can get almost anything on the floor and throw it at your enemies. You can't kill enemies with jumps to the head anymore. You have to throw something (or even the enemy itself, if they're small and light) in order to kill them. And everytime you leave an area, they'll respawn, giving you much more frustration than joy while playing it. The environments still greatly colorful, thought its desing is relatively ugly when compared to another Mario Bros games.
The soundtrack in this game, unlike its predecessor's, is totally ridiculous and take the already bad feel of the game. The songs are good, but they just don't fit with the backgrounds, due the background's design drastic changes. The sound effects are also really bad, taking the Mario feel away from the game even more.
At least, the gameplay holds up pretty well, since the controls respond quickly and they're easy to learn. Though, they're not that perfect, since you'll be confused at some times with the controls.
In the end, Super Mario Bros 2 is a good game, nothing more. Its lack of the real Mario feel and the drastic changes didn't make the cut. This game proved Nintendo that good games don't need to change to keep up with the times. If you're looking for a good platform game, check this one out. But if you're looking for a Mario game, try the original Super Mario Bros. Good game, bad idea. This resumes Super Mario Bros 2