I've played the original Mario Bros. quite a few times over the years, especially since it's made an appearance in the original Super Mario Bros. 3 as a little extra, the GBA Super Mario releases, and more recently, the first NES Remix game. I had a copy of the original NES cartridge, and gave it a closer look than I have before.
The game is typical classic arcade goodness. The jumping is a bit stiff (although not nearly as bad as the generally frustrating Ice Climber), but the game is meticulously designed. There are only three types of enemies (Shellcreepers (turtles), Sidesteppers (crabs), Fighterflies flies)), but they all have unique movements, and the progression of levels is smooth. The stage layout itself doesn't vary, and there are only twelve unique "phases" (i.e. stages), but things get pretty hectic once the number of enemies in a stage increases. The game also has several hazards, namely red and green fireballs and "Freezies", blocks of ice that coat part of the stage with ice, making the ground slippery. The game has two difficulty levels and also has a 2-player mode, in which you can co-operatively progress through stages, or purposely try to trip up the other player.
As with games of the era, getting through the first twelve stages isn't that challenging, but there's plenty of challenge in shooting for a high score. This was a fun blast from the past and fun seeing all the connections to Mario games, such as Freezie and the POW block, and at some point I'll have to try out the original arcade version, which was released on Switch last September.