If it concerns you, I do spoil some of the endgame information of the module, so be warned.
I think this really is one of the best starting adventures for D&D. You get a town, a mystery, some wilderness exploration, and some not-too-big dungeon crawls. This being an older adventure for 1e, it will require some not insignificant fixes and tweaks. You'll need to figure out stats for NPCs like Father Abramo, Misha Devi, the evil monks, and others, and you'll need to make some serious tweaks to either the 1e spirit naga or the 5e spirit naga to make the final fight both fair and challenging. Fortunately, conversions do exist online that you can use to aid this process.
Additionally, the module probably will have more magic items than your players will know what to do with if you leave it unchanged. While I don't think you should excise them all, as I think even low level player characters should have a handful of interesting magic items in order to evoke excitement and awe at the world's magic, I would advise that one exercise a smidgen caution about how many items they leave in.
Finally, I remain wary of any module that recommends that a high level NPC tag along with the party, as Against the Cult of the Reptil God does with Ramne. However, when I ran the module I was able to simply leave Ramne out (well, the party found him dead, killed by the cult), and they were still able to successfully maneuver the lair of the reptile god. The module even has recommendations on what tweaks to make if the party goes without Ramne.
Overall, Against the Cult of the Reptile God is a great starting adventure, and I'd recommend it to any DM interested in taking the time to work with the module to make it function for 5e (unless you're running a game of AD&D, in which case you're good to go and more power to you). Make the module yours, and you and your party will have a good chance of having a great adventure with a little intrigue, a good heart, and plenty of adventure and danger!
[5 of 5 Stars!]