This was one of three video games that directly steered me towards role playing. We had an Apple IIe for quite some time growing up, so the number of games available to us became more and more restricted as we aged. The Zork franchise stuck with us longer than most, though, all the way to Zork Zero. I stuck with it all the way, mainly because it was damn near impossible to defeat (no way was I calling that 900 number to get hints!).
Interestingly enough, it was that impenetrability that drew me in, and kept me coming back to the game. It's one of the few games actually feels like an old school RPG. I just didn't know it at the time.
Full of vast underground empires, magical artifacts, spells, humor, Zork had it all.
Almost... too much, though, at times.
The series could be positively labyrinthine. My favorite example of this is from Beyond Zork, where you need an ancient artifact, the Pheehelm, in order to be intelligent enough to read word that opens the door to the last area of the game. In order to get the helm, you need a minx (found by wandering in the forest until you come across a band of hunters chasing one, which you save), an hourglass (purchased for 1000 zorkmids, which you can only obtain by selling a huge gem, which you get by making a mother hungus chase you towards a statue. She charges you, hits it, it falls into your lap. Don't ask what a hungus is.), an ever-fresh truffle (minxes hunt for truffles, find one, then wade into the pool of Youth (found in another area), and the truffle will never age). Now you go, stand under an arch and turn the hourglass, which takes you back in time, to the last time the Helmet (remember the Helmet?) was seen, in a vicious battle between the forces of Pheebor and Borphee. A prince is wearing the helmet, is decapitated, and his head falls into a trench. Can you pick up the helmet there? Hell no you can't! You throw the ever-fresh truffle into the pit, then turn the hourglass and go back to the future! Your minx (remember the minx?) leaps from your arms, and digs through the earth, finding the ever-fresh truffle, and, HEY! It's the Pheehelm!
Take a moment to reread that paragraph, and try and comprehend how much trial and error, how many "You can't do that here"s you would have to go through, in an ALL TEXT adventure, before you figured it out.
Trust me, the Tomb of Horrors ain't got nothing on Zork - by the time I cracked the Player's Handbook for the first time, I was primed and ready for D&D.