Like its Apple II counterpart, AtariSoft's Commodore 64 port of Mario Bros. was never officially released. Unlike the Apple II version, however, the Commodore 64 game reportedly was still in development when cut from Atari's line-up. That leaves this port good instead of great. What's here is well done, but what's missing makes for an incomplete experience.
To list what's missing, there are no "large" fireballs, Slipice never freezes platforms, and there are no icicles in the later levels. Actually many home versions of Mario Bros. are missing the icicles, but unlike those other versions, the Commodore 64 game actually turns the upper platform blue, warning of the icicle threat, just like the arcade game. Despite that warning, no icicles ever appear.
Fortunately, pretty much everything else is in place, and again is well done. Atari was on their way to creating another winner for the Commodore 64. It's a shame they felt the need to kill this port before its completion.