You mentioned Inform! My life is complete! I can go all whiny fangirl and snobbishly complain that TADS is far superior if you'd like, though.
Text adventures in general are awesome, though. They're much easier to put together than a graphical game, even if you use a more difficult language like TADS, so you can focus on creating good gameplay and story rather than worry about physics engines or graphics.
(for the uninitiated--Inform is more of a scripting language, while TADS is more of a complete programming language, just specifically geared toward the creation of text adventures. As the joke goes, TADS is so powerful, you could create Inform in TADS! Both are very powerful, however, and you can make complex, fascinating games in both. If you've never played a text adventure, first, I pity you. Second, check out Dreamhold [http://eblong.com/zarf/dreamhold.html] by Andrew Plotkin--it's a great introduction to the whole thing, and it's a wee bit easier to figure out than something impossible like Hitchhiker's Guide to the Galaxy [http://www.bbc.co.uk/radio4/hitchhikers/game.shtml]. When you're done with that, there's thousands more at the IF Archive [http://www.ifarchive.org/] (as it's rather a large place, you might be better served by looking at Baf's Guide to the IF Archive [http://www.wurb.com/if/], which categorizes and reviews many of the games in the Archive).
If you're interested in writing interactive fiction on your own, why not check out TADS, Inform, ADRIFT, or one of the other many free IF creation tools out there? If you'd like to learn about TADS, check out the official site [http://www.tads.org/], where you can download it for free and get some really great literature/tutorials [http://www.tads.org/t3doc/doc/index.htm] to introduce you to it. Inform can be found here [http://inform7.com/] and ADRIFT (another relatively simple system) is here [http://www.adrift.org.uk/cgi/new/adrift.cgi]. If you want advice on writing text adventures, there's some great articles over at The Brass Lantern [http://www.brasslantern.org/]. Enjoy!)
I'm a little obsessed with these things, can you tell?