I want to first say that I wanted to like this book, especially because it's such a bizarre mystery story. I also had a bit of nostalgia for Who Framed Roger Rabbit and knew that it was largely inspired by this book, and I was fully aware that the book and the movie shared little in common when I started reading.
I don't mind that. I love when people take creative liberties and create something wildly different from the inspiration a piece of media gives them, so my issue isn't even that I wanted it to be the same.
My issue is that it really does have some great potential, and you can see how someone was able to create the movie from this book (and holy shit were we lucky that the movie was pushed in the direction it went because this Eddie Valiant is so bloody frustrating, while Bob Hoskins' rendition of the character is just so well done and likable despite his somewhat grumpy nature). There are a lot of cool elements of the plot that are actually an interesting story, and the solution to the mystery is both very easy to piece together but still hidden enough for it to not feel either too simple or too obtuse; it's definitely within the realm of possibility.
But I hated so much of the presentation, especially because it kept hitting some really messy messaging. Toons seemed to take the place of any person who was either non-white or poor and rural (or both). There were bouts of misogyny related to the only two women in the whole book (Jessica Rabbit and her previous job related to sex work, especially), and there was a hit of casual fatphobia for a Persian belly dancer who Eddie ran away from because of the "size of her belly."
You really can see where a lot of the inspiration comes from. Like, I suspect the aforementioned belly dancer was morphed into the Hyacinth Hippo (from Fantasia) that appears in the movie instead. But you can certainly see how they recognised what would make a better story with a few of the same characters (Eddie Valiant, Roger Rabbit, Jessica Rabbit, and Baby Herman) and a change in setting (from the 1980s to the 1940s). They also found a much better use for the humanoid Toon gimmick (in Christopher Lloyd's portrayal of Judge Doom) than was done in the book, though that gimmick is quite fun in both.
But I do wish that this guy had thought more about what he wrote because the story is pretty good, but the way he handled so many topics is just... fucking obnoxious and it really feels like the book is the author's tone because of how much book-Eddie feels like such a self-insert for him (which is not helped by the fact that Gary's in both the front cover art and the back cover art). Like goddamnit, I really did like that the ending was... not what most people would want? But it still felt right.
You could really see the interesting bits of the story! Genuinely. But its pitfalls are really obvious, too.
(Also, instead of having Benny-the-Cab as a Volkswagen Beetle, the Bennie in the book is a beetle who collects literal junk. Both are okay, but it's just very funny to me.)