First published in 1982, Douglas Niles's Against the Cult of the Reptile God is the first of five "Novice" adventures written for AD&D over the next few years. Designed for 4-7 characters of levels 1-3, the adventure is written for novice DMs and players. It is set in the village of Orlane in the World of Greyhawk, and concerns a cult who are charming and enslaving the villagers. With any luck, the characters will arrive in Orlane, do some investigating, find the cult, and stamp it out. What could go wrong?
Well, quite a lot, actually. The adventure is the first (predating The Assassin's Knot by a year) D&D adventure to use investigating a mystery as the chief driver of the story, and so Niles didn't have many previous examples to draw on for inspiration. Call of Cthulhu stories are mostly investigations, and had come out the previous year in 1981, but few adventures for it were available when this adventure was published. In my experience, investigative role-playing is an extremely challenging style of adventure to run and design. So, the choice to use this style for a novice adventure is extremely questionable. You could have gotten away with it with a lot of advice as to how to shape the adventure, but that advice is lacking.
What you have is a description of the town, in the same style as The Village of Hommlet, including more detailed description of the two inns, and a dungeon where the cultists hang out. It feels very much like The Village of Hommlet, but with this additional plot line of active cultists added in. The basic material is far stronger that that of Hommlet, but it is a bad fit for novice players.
Wizards of the Coast combined this adventure with Hommlet and Keep on the Borderlands for their recent D&D Encounters season of The Village of Hommel Lane. It makes for an interesting comparison. Hommel Lane is so much easier to run! The big difference is that Hommel Lane has event-based encounters, a proper beginning where the PCs know there is something wrong and get it demonstrated to them very early on, and the adventure suggests a number of routes that the players could take through the adventure. That last is tremendously helpful, and it's lacking here.
So, given that the novice tag on this adventure is extremely misleading, how does the adventure play with experienced DMs? Well, better, but the final lair of the cult has some deadly encounters; unbelievably so for a group of first level characters. How well will they fare against a fifth level evil cleric and a wight? The cleric they could defeat, but the wight? If it hits any character, they're basically dead (energy drain), and silver or magic is required to hit it. Then you have the final encounter, with a spirit naga that can cast fireball! First level characters are not going to survive that!
The adventure is aware of that, and assumes the group enters the final encounter with the aid of an elderly village mage, who can cast lightning bolt and globe of invulnerability to aid the party. He'll need to against the naga! However, this betrays the actual accomplishments of the party: they've found the Big Bad, but they need a NPC to finish it off. The module recognises that the mage could overshadow the PCs and recommends that you be careful, but the design then requires him for the final encounter! Not good.
Ultimately, the concept behind the adventure is great, but the execution relies heavily on the DM. It really feels more like a 3rd level adventure that was rewritten when TSR decided they needed to start up a Novice line of D&D adventures, which left a few holes as a result. There certainly isn't enough advice for the novice DM, which is something that Keep on the Borderlands got a lot closer to right. So, it is a flawed classic, misleadingly labelled.