This was a lot of fun! Very theme coherent - blubbering sad fungi everywhere. Talking shrooms. Light-heartedly weird tone. Weird effects, mutations that can happen to characters who ingest shrooms. Treasure is often more interesting and twisted than a pile of coins- "Is this a 'potion of flying' or 'dying'? The label is hard to make out..." "Pickled, Evil Remains", "cracked wine glass which fills with sweet wine if repaired"
Guy Fullerton, who created deservedly well-reputed OSR-type adventure Many Gates of the Gann, and pretty much wrote the book on good design (or rather the chaotic henchmen blog posts) provided feedback (along with several other bloggers and other people) to Karl Stjernberg in making this.
The format is generally clear and the writing is brief but evocative. The OSR-friendly, easily-converted nature of the stats were no trouble, easy for someone with a 1e/S&W/Labyrinth Lord outlook to understand.
Minor quibbles: I wanted some of the monster stats closer to where the monsters are encountered in the text of the adventure, or at least referred to with (stats on page whatever). I was also disappointed not to find undead axolotl stats. I wish the "Black River" and "Where Does the River Go?" sections had not been left for GMs to flesh out like Keep on the Borderlands' "Clearing this tunnel out could lead all the way to Cave of the Unknown, which should be stocked..."
The art is great, and contributes greatly to the fun tone. You can almost smell the funk and feel the wet squish of the shrooms and hear the schlorp of the schleim! The adventure is formatting a very print-ready layout. I usually don't care about printing pdfs but this one I will. On paper, on your bookshelf, it'll look like a zine or underground comix thing.
I also like Karl Stjernberg's character sheet design, which is available for free download as a separate product. It provides a sort of preview of the style of art in Spores of the Sad Shroom.
Very much looking forward what oozes out of Stjernberg's brain and pen next!