The cover is great. I love the extra little touches to make it look like an old paperback.
Honestly, all of the aesthetics are great. The cream-colored paper, the font choices, the art. All great.
Incredible job of laying out an interesting dungeon (although that brain is not where I'd expect it to be) in one page and change, along with an evocative map and a single page of background and interesting monsters.
I don't see a system stated anywhere in the PDF. Is this for Cairn? A delightful adventure, no matter what.