About the "secret mode", I remember the first time I saw it: The on/off switch was wearing out, and between the off to on transition occasionally made false contacts. The first game that acted weird was Raiders of the lost ark.
I think it was an electrical problem related to memory refresh, since first you had to turn the Atari 2600 on, then quickly poke the on-off switch to make it do a fast off-on cycle. Sometimes it did garble the game. Strangely enough, it could be garbled several ways, but the playable one was always the same. For example, Raiders of the Lost Ark would show the ark elevator with a lateral offset (Can't remember if left or right) in the opening screen. There were more alterations, but I can't recall them.
*Sigh* Man, those were good times. Looking for that old game node here reminded me when I was a 12yo, proud of my +50 black cartridges collection, all neatly piled up, with their top-side white-on-black bold-letters titles perfectly aligned. There were some colored or odd-shaped cartridges, but I kept them locked in a briefcase because they weren't as neat as the Atari standard cases... *sigh*
My favorite solo games were Demon attack and Yar's revenge. And Combat, Asteroids and Space War when there was company. Still today, my left thumb is about as twice as fast as my right one when hitting a button repeatedly.
I believe the gaming experience a 2600 gave was something unique, never to be repeated again. The games were simple and quick to learn, the game play was fast. What made them shine was the difficulty grade (for such a primitive console, you won't believe how hard some games were), the imagination of the player that filled the gaps between the booklet and what actually appeared on the TV, and my worst addiction, the one million score quest.
The king is dead. Long live the king!