For those of you who didn't know Atari and Nintendo used to be big business partners back in the day. Ports of Nintendo arcade games sold very well on Atari systems. Nintendo even approached Atari as possible distributors of the NES.
Anyway I was expecting a crapola port after the fiasco that is 2600 Donkey Kong, however I must say this is a decent arcade translation as far as 2600 games go. All of the gameplay elements are there, Mario knocks over turtles, crabs, and fireflies by punching them under the floor, you collect coins, fireballs chase you, and the slipice monster freezes the floor up and makes you slip and slide. This version even supports 2 player simultaneous play (a big deal for the 2600.)
Although all of the elements are there, none of them look very good. Mario has maybe three frames of animation. He does look a lot better than 2600 Donkey Kong Mario though. One of the problems the 2600 has is that it can't display sprites in more than one color. So the trick to give Mario and Luigi different colored shirts and pants is to split the sprite in half (you can see the divide when Mario runs as part of his arm becomes blue.) A pretty imaginative workaround for a machine as limited as this. The coins that come out of the pipes are also square for some reason, but they still flip as they move. The floor also doesn't bend when you punch under it. All of these little things don't really detract from gameplay though.
What does detract from gameplay is crappy collision detection. Yeah, the collision is alright when you punch a turtle from under the floor. But all you have to do is be in the general vicinity of an enemy to get nailed by one. One of the things about the arcade game was you could hit a baddie off of the edge and nail it while simultaneously jumping onto another level. Sadly this is too complicated for the 2600 version. The bad guys only flop upside down in one place. Another thing was that if you timed it right you could run under the fireballs. None of that here. Also you can't jump on the POW block, which admittedly is a small gripe but still that's like the one "safe" area you have on the whole board.
Despite it's graphical and collision flaws this version of Mario Bros. is pretty solid and is definitely one of the more impressive games in the 2600 library.