MuhVerisimilitude
Hero
Big fan of books that inspire adventure. So... Nobilis rulebook. 2nd edition. It oozes creativity in just the right way.
Big Blue was Champions:View attachment 350472
the non-Champions HSR4 core was this:
View attachment 350471
And about half the thickness.
Gotta get your chainmail bikini from somewhere!
It can be a core rule book, an adventure, a setting guide, a splat book, or even a tie in novel or comic book. What book directly related to TTRPGs is your favorite of all time.
You can use whatever definition of favorite you want, and of course your criteria are your own, but let us know the details!
I am going to pick Aaron Allston's Strike Force. That book was not just fun to read and about/a supplement for a game I love (Champions) it literally opened my mind about what a RPG campaign could be. I love that book so much I refused to buy the update because I didn't want to mar my memories or experience with a bunch of after-the-fact essays and such. (One day I will probably pick it up, tho.)
The Pavis and Big Rubble boxed sets are both good, but I'd personally pick Trollpak over either. But if there was only one Runequest product I could pick it'd be Shadows on the Borderlands, which I don't think has been matched as a collection of adventures.Well, they are bound into a single volume now, but I think at least one of those boxed sets would qualify as a single product. I'd pick Pavis over Big Rubble for The Cradle scenario.
1e Deities & Demigods. Yeah, the 1e DMG is up there, but this is the one that really captivated my attention when I was a kid.