I downloaded (and had initially intended to buy in print) this adventure based on a smattering of online acclaim that it was the adventure to use to teach players new to the OSR style of gaming. It is system neutral and can easily be ported to the old edition or retro clone of your choice. This portability is the only good thing I can say about Tomb of the Serpent Kings. (Besides it being free to download.)

For all the set dressing involving sorcerer serpents and such, this is a pretty boring dungeon. It's got all the complexity of the sample adventures you can find in the old red Basic player's manual. The author intends to teach "lessons" about OSR-style play, but mostly these lessons are taught by smacking the players in the face with it and shrugging its shoulders, because OSR.

While there are some nonstandard original monsters at the end of the dungeon, I found it to be too little, too late. In fact, the group I tried running it for (Pathfinder players interesting in trying old school rules/playstyle) were ready to quit not even halfway through.

There are better adventures to use if you're planning to teach some new players the ropes. This seems couched firmly in the idea that OSR play is hardcore and the players have to learn the hard way. The tone comes off as condescending and spiteful. ('Dungeons contain undead, and undead are dangerous!') Hard pass on running this for players new to OSR style stuff in the future.

I like this dungeon a lot. It was the first OSR thing I ran, and the first RPG experience for a dozen or two people who played with me over several runs. It has been very successful in putting my players into the OSR mindset; the first level (about 7 rooms) sets expectations for the rest of the dungeon perfectly, making players treat everything they find as both potential threat and potential treasure.

The first level and a half is somewhat linear, but the dungeon opens up pretty quickly after that. Some of the things in the dungeon are brutally dangerous, but that won't come out unless your players are constantly aggressive, which is good fun either way.

If nothing else: the PDF is free. Just grab it. The worst case scenario is that you delete it and forget about it.

Don't listen to the hype, this isn't worth your time. It's a railroaded dungeon with high-lethality traps that have no warnings and "lessons" which either don't come up or aren't clearly written. Skerples has been asked about why the encounters fail to communicate lessons and dodged by saying that not ever lesson in his training-wheel railroad dungeon needs to be learned. But if there every lesson doesn't need to be learned why are you playing/running a teaching dungeon instead of a regular dungeon? What Tomb of The Serpent Kings does teach is to play in that particular flavor of False OSR full of "gotcha!" death traps and "deep" but pointless fluff.

Could it be fixed? Yes, but so could N1 and Castle Spulzeer. By the time you're done "fixing" TOTSK you might as well have written a new module