[ghaff]

Planetfall is another by the same author as Hitchhiker's Guide to the Galaxy, Leather Godesses of Phobos and A Mind Forever Voyaging. AMFV doesn't get the love it deserves. It is more about real interactive fiction than puzzle solving. Hitchhiker's is enticing but pretty difficult--not as big an issue perhaps these days as it's so easy to "cheat" if you get stuck as opposed to calling the author :-)

Trinity is another good one. As is The Lurking Horror--set at a thinly-veiled MIT campus where many of the authors were from.