I think White Wolf was the Queen of this back in the 90s.
Changeling: The first softcover edition was particularly fun to read, as were the other books in the line. It was kind of "emo lite" to things like Vampire.
The problems, however, are numerous. For example, in the soft cover book, you used cards to cast spells (glamour). The problem was that the book encouraged the Storyteller to make their own card, but provided few examples or guidance. You could buy cards, but they weren't carried in many places and were akin to trading cards sold in packs, IIRC.
The hardcover changed the glamour system around quite a bit to fix that problem, though.
White Wolf als published this awesome book called HoL: Human occupied Landfill. The book was hand written. Let me say that again, it was hand written. At one point, the author had the waitress sign the book to prove that he was at IHOP. Its in the book. Frankly, I don't remember there ever being any game mechanics in the book, despite it starting out saying that it was a roleplaying game.
TSR's Planescape was also, to some degree, more fun to read than to play as written. While not as bad as HoL, it lots of playable ideas, some of the proposed mechanics seemed a little off to me. I think this was because they had problems with things like the silver cord from from the regular game. Of all of TSR's games, I think it was the most White Wolf like. It's why I loved it. That said, I will always thank the Planescape team for giving us Sigil and the Lady of Pain.