Anyone who is in to Atari 2600 knows that ET is verrrrrry far from the worst game available on that system! And it's so sad making it a great game would have take so few tweaks! http://www.neocomputer.org/projects/et/
An initial run of 4 million copies is a lot of pressure on a single developer, the sort that can make you a legend or a catastrophe. I wonder if release management was considered to allow for bug fixes in subsequent production runs or phased production runs with hedged risk.
Probably adding to the pressure is the frustration that immediately following the production run you find a one-liner bug fix but you are 4 million copies too late.
Interestingly, Pac-Man also had millions of unsold cartridges left over. This candid Q&A talks more about the failure of ET, the frustrations and challenges:
http://www.denofgeek.com/games/howard-scott-warshaw/33708/ho...