The art in the games of the 2600 is the gameplay itself and the experience that it gave you, not how pretty it looked. Look at the popularity of the casual games of today, sure they look better, but gameplay wise are they all that different than the 2600 in terms of gameplay?
Angry Birds would be an example. The concept is simple, break stuff to kill pigs, then try to get 3 stars. The gameplay mechanic is simple enough that anyone can play it, much like a game on the 2600. And it has a score system, like a lot of casual games do. Does it look better, well yeah it better but at it's core it's the same type of game that you would have seen on the 2600, and that's the beauty of the 2600 and that age, the simplicity and addictive nature of the classics of the era, the same principles carry on today.