gamefreak1972: I've got very fond memories of these games, and text adventures overall. I certainly wouldn't mind seeing a collection of text games available; not just the ones by Infocom but I seem to remember a fair number of other ones around the same time. I vaguely remember some for the Vic-20 like "treasure island" "the count" and "adventure" I think...
Anyway, the question: I only ever played the first 3 zork games, but none of the ones after - is there a particular order they should be played in? Yes, I could google it, but I wouldn't mind hearing some opinions. :)
The actual sequels to the text adventures were Enchanter, Sorceror, and Spellbreaker, and Wishbringer was also part of the series. After the first 3, Beyond Zork is a good choice, although it is quite different with some RPG aspects and a map rather than straight text adventuring. Zork Zero is also a text adventure, albeit with some illustrations and graphic mini-games. It's interesting because it tells you some of the history of the world.
After the text games, go to Return to Zork. This one angered many people because they abandoned text for graphics, but once you get into the strange puzzles, wild humor and quirky characters, all will be forgiven.
Next, go to Zork Nemesis (I think of it as Zyst Grim-e-sis) since it is very much like a grim version of Myst with a bad attitude. This one is very dark, and it doesn't relate to the games, but to an obscure set of choose-your-own-adventure type Zork paperback books. (Of course if you read those books you will be horrified by the terrifying and grim fates of the book characters when you find them in Nemesis).
Also, this one's got some scenes that will have you looking over your shoulder. This game will likely frighten you at least half out of your wits.
Finally, check out the other side of the Z-coin, Grand Inquisitor. After the grim Nemesis, this one's a wild slapstick adventure that relates closely to the known Zork universe, and it's the complete opposite of Nemesis. This one's probably the silliest comical adventure you'll ever play, and it ends Zork on a fun, hilarious note.