Can’t remember any particular performance problems with ET - it’s no more flickery than any other 2600 game, sound plays fine, screen changes when you fall in a hole are prompt, all that kind of thing. Now, utterly bizarre and unintuitive gameplay, yes; it has that in spades. Also quite unfinished, but Howard Scott Warshaw only got five weeks to develop it so I’m prepared to point the blame at Atari for that.