I never owned a NES when I was young, so I have not played Super Mario Brothers extensively before. But we did have a Commodore 64 at home, and we had much fun playing Gianna Sisters, which is, if I recall correctly, a vamped-up clone with the exact same gameplay.
These days I do have a NES and I do own a copy of Super Mario Bros, and playing through it for some research, the game got me hooked (again). Sure, in many ways this oldie cannot compete with more recent games, but it crafted a genre out of nothing and in its purity the game still rocks. It is amazing how well designed the game is, considering the restrictions of its day and age. It is not difficult to play, but without a save game, it is a hard game to complete (I have not yet succeeded, although I finished Gianna Sisters dozens of times). Compared to contemporary games that have many more levels and obstacles but which are also much harder becoming unplayable without the quick-save option. As a result the game is much more accessible to non-gamers (my girlfriend likes this game too) and much more attention can be paid to tweak the gameplay of the levels as they exist. Talk about replay value. To win this game you really need to execute a stunning performance, which gives you a totally different sense of accomplishment, than completing a game after 40+ hours spend over multiple sessions and millions of save games. To be sure, you cannot make commercial games like this anymore, expect maybe for the Internet, but is nice to see that the quality of an old game like this still shines through.