Medusa's Gold

Obviously, we're biased (we wrote it, after all), but we think Medusa's Gold is a great introductory IF book.
Let's be clear—This game is extremely merciful indeed. In fact, if Merciful was a person, it would most likely be voted Mayor of IFington-on-Sea.¹ Sure, failures may push you back a few locations, but you cannot die, there are no complicated combat mechanics,² no dice rolling, and no character sheets or inventories to maintain.
All that said, Medusa's Gold is still a detailed, 750 location/110,000 word³ romp with four distinct paths (and numerous sub-paths within those) that has its tongue planted firmly in its cheek. So expect copious footnotes, fourth wall breaking, and a plethora of (subjectively) hilarious escapades that combine the simpler style of CYOA, FF, and other early IF games with the delightful absurdity of a carefully crafted Monty Python sketch.⁴

^{¹ Or possibly Deputy Mayor, depending on the recount—it was a close contest.
² It uses a simple 'learn the sequence' system that is so simple, even the author could use it.
³ ...ish.
⁴ Definitely one of their less well-known sketches, written on a wet Tuesday, around 4:39pm, where John and Eric have failed to turn up, Michael has a bad cold, and both Terrys are distracted by a small halibut that they recently discovered has been living in the kettle.⁵
⁵ Nobody knows where Graham got to that day.}