For those wanting more frotz games to try, please know that there are TONS of freely available games written by the interactive fiction community. Also, many of them are of a higher quality and more fun than the stuff infocom produced (the genre was in its infancy then).

See this site for more general info:
http://ifarchive.org/

And for finding actual games, this site is very good:
http://wurb.com/if/