After going on a gamebook binge I've become really picky. In a traditional gamebook you not only have to write a compelling story, but build a world, allow choice, and then there's the whole "game" part. It is a tough and delicate balance that most books simply miss.
Morris is the best writer of interactive books I've ever read. He can make me go from "this sounds awful" to "WOW!" in a few sentences. It is a captivating magic that I'm still in awe of.
Castle of Lost Souls is about a man who made a deal with a demon and rich sons who are looking for an adventurer (You!) to help his soul escape captivity. The story sounds silly in my summary, but Morris makes it work, bringing to life a playful expanse filled with secrets. You use typical gamebook items, like dice to battle against evil, as well as a character sheet to track your plunder.
It can be beaten in one sitting, but is worth a second play through to see some of the other encounters you can have. What strikes me is how the author is always mixing up your expectations, both narratively and within the game. Just when you feel comfortable he changes things in clever ways.
While many will likely ding this gamebook due to its shorter play time and reduced length (300 sections), I personally think that's its charm. It doesn't overstay its welcome. Much like a good friend, it has fun, but knows when to leave.
I didn't expect much from this book, but it was a quick, joyful read that is far ahead of most gamebooks available.