I remember a specific subgenre of those: roleplayers get sucked into their own game. Sometimes the GM was complicit, and sometimes he/she wasn't. I don't know if the idea started with the Dungeons and Dragons cartoon, but judging by the dates on some of these books, it really took off in the eighties.

From what I recall it was less about wish fulfillment and more about the characters thinking that's what it would be and having that belief bite them in the ass because the world they were in was darker than they bargained for.

I'm sure some were wish fulfillment. They're just not the ones that come to mind now.