Matthew Finch is one of the more prolific authors of the OSR, and consistently seems to produce some quality product. I picked up Tomb of the Iron God as part of a bundle deal a while back, and it was one of the first things I read from it.
Villagers report a truly massive lightning storm centered on the nearby Monastery of the Iron God. The peasants believe the Iron God -- a largely forgotten minor deity of the underworld who guards the spirits of the dead -- destroyed his own monks to punish their greed. The peasants claim the heretical monks had been accumulating great treasures. They've seen no sign of the kindly monks since the storm.
If it was indeed divine wrath that destroyed the monastery, then its treasure-laden catacombs are obviously fair game for an enterprising group of young adventurers such as yourselves.
This is an introductory adventure written specifically for Swords and Wizardry, but easily playable with any old school edition of D&D.
This is just about everything that an introductory adventure should be. It's got some solid background that is interesting and easy enough to drop into almost any sandbox without problem, with the potential to drive future adventures, depending on the actions and success of the adventurers. There is a rumor table though it's highly skewed toward one answer over the other. I'd add to it to balance it out. The wandering monster table is nice in that it shows the maximum number of possible encounters of each type. The numbers are such that you probably wont run out, but it's a nice touch.
Another feature that I like is that each keyed room there is a notes box provided, so you can track what the PCs do, either for an after action write up, or to restock for followup visits. There is a good variety of things for the PCs to encounter, puzzles to figure out, traps to avoid, monsters to fight, and even a pair of gods! You've got to love an intro adventure that doesn't pull it's punches. Granted, they're both more like godlings, but still, it's an impressive choice, and one that would be hard to pull off.
One of the best things about this adventure is that it's clearly written to be used. Background is kept to a minimum, descriptions are utilitarian, or skipped to allow the DMs to flavor it in a way most appropriate for their table. There is an entire section in the back to restock the dungeon, both with all new and different monsters and new treasures, plus a half a page on how to run the adventure, should you be new to running old school adventures. I really like how that's at the back too, since experienced DMs don't need it, and new DMs will have theoretically read the adventure before
The dungeon is on 2 levels, and the 2 maps that show them are clear and easy to read. There is only a single image in the adventure besides the cover.
This has the feel of a truly classic intro adventure, and I am definitely going to keep this handy he next time I get to start a new game.
I have the PDF, which I printed out in booklet format. It's 28 pages long, plus the cover. There are 58 described locations, as well as the items noted above.
You get get a copy from Lulu, and if you're starting a new campaign, this would be a great place to start.