This adventure is an excellent throwback to the old days, or it’s part of the new OSR movement, all depending on your perspective. It is easily adaptable to various iterations of D&D or Dungeon Crawl Classics Roleplaying Game, but is system neutral and the mechanics lend themselves to straightforward conversion.
This is the first level of Frank Mentzer’s megadungeon, and it’s quite sprawling with a variety of encounters, wandering monsters, and puzzles. Further levels would certainly be something to look forward to in the future but there is material here to last a group of old school delvers quite a while and cause a casualty or two (or six).
For more of my thoughts on this product, a longer review is here: