The most striking difference is the speed -- no longer is Mario's climb such a tedious chore. He scoots along the girders and up the ladders with ease, and you don't have to struggle to find the bottoms of those ladders. Audiovisuals are also superior in every way. The barrels roll down with fluidity with zero flicker, and Donkey Kong himself jumps up and down on the girders if you don't start the game in a minute and 13 seconds. Furthermore, the girl now looks like she might almost be worth rescuing, and she shouts, "HELP!"
While the Atari Computer cartridge version of Donkey Kong wasn't the most publicized home edition of Shigeru Miyamoto's classic, those who have experienced Atari's translation know that they're playing the best version available on a classic machine.