If you loved the old Infocom stuff, you'll fall head over heels for the great stuff that has been released - non-commercially - by game authors over the past decade. Here's a few suggestions:
Slouching Towards Bedlam - Winner of the 2003 IF Comp. Saying too much would spoil it, but I will say that it involves kabbalism, steampunk, and Victorian England.
Photopia - Standardbearer for "puzzleless" IF. The game limits your input, but you won't care. A tremendous story.
Galatea - The game that revolutionized NPC characters so much that no one has dared attempt anything similar. Truly astounding.
For more on what's been going on, check out Baf's Guide to the IF Archive -
http://www.wurb.com/if/index - particularly the section on the winners of the annual IF Competition (games intended to be played in less than two hours) and XYZZY Awards (best IF of the year). The links page also has many sites listed of regular newsletters and other info on the current state of interactive fiction.
Also check out Nick Montfort's book, "Twisty Little Passages", just published last November by MIT Press. It's a grand survey of IF as literature, and has enough history to sate your appetite. Or, more likely, whet it.