I played ET as a kid when it came out and then many years later. It was a massive disappointment when it came out - it made no sense, and of course it had those infamous pits. When playing it as an adult, I realized it wasn't the adventure game it looked like (and arguably ought to have been) but rather a fun little puzzle game. An interesting novelty, and flaw for a mass market mainstream game, was that the printed manual was an integral part of the game. Without the manual to look up the cryptic glyphs that would appear on screen, the game truly made no sense.
So most of the ET demographic (young kids) played it without really playing it... wandering around what seemed like an adventure world (a la 2600 Superman or Raiders), not even noticing the glyphs, and certainly not working out the glyph puzzles using the book.
ET really wasn't that bad of a game once you RTFMed. Definitely not the worst. The 2600 had so many awful games that were worse.