This one is tricky because I never liked fiction based on a roleplaying game. I mean, yeah, as a kid I discovered Dragonlance long before I played Dungeons and Dragons, although I knew that they were somehow related. I also liked some of the Ravenloft books, but in retrospect they weren’t really all that great.
So I don’t really have an answer. So I’ll cheat!
My answer is Mouse Guard. See my post about it here.
How does that count? Well the author wrote the first volume based on a D&D campaign that he and his children had played with mice instead of humans, elves and dwarves. Also, the subsequent volumes of the comic were influenced a bit by the RPG that was developed after volume 1.
Mouse Guard is well written and beautifully drawn. The backgrounds themselves are incredible: so much detail, but not overwhelmingly so.
Other than Hellboy, Mouse Guard is my favorite comic book series ever. Every single volume is perfect! I recommend them all, especially The Black Axe.
So that is my answer. Kind of cheating, but I can’t respond otherwise!