Parents should know that kids younger than 10 will have a very rough time completing Super Mario Bros. 2. It is an exceptionally difficult game, and kids may tire of it quickly. But they shouldnt worry about the content—theres no blood or death, with defeated characters flying off screen.
Fans of Super Mario Bros. 2 will get almost exactly the same game as Super Mario Bros. 2 on Super Mario All-Stars. There are a few new graphical tweaks here and there and a Yoshis Egg challenge after you beat the game, but there are no new levels nor any new exciting elements.
Fans of Mario Bros. cooperative play should write nasty letters to Nintendo for forcing players to own multiple copies in order to enjoy it. If you have friends, roommates, siblings or cellmates with Game Boy Advances it could be worth it to consider splitting the cost of the game to play the Mario Battle mode, which simply can't be missed.