For further reading, I'd like to recommend the book Let's Tell a Story Together: A History of Interactive Fiction by Jimmy Maher. It is available for free from the author (in Kindle format or readable online): http://maher.filfre.net/if-book/index.html

The same author has also written many great blog posts walking through the history of interactive fiction http://www.filfre.net/about-me/sitemap/

His article about Ultima IV got 97 comments the last time it was submitted here: https://news.ycombinator.com/item?id=8020954