Your prompt doesn't seem to actually allow for any critical thinking development or give any guidance to how you can more convincingly express your points or arguments. It also assumes you didn't enjoy the book, which I'm sure some students would have actually enjoyed, so now your prompt is even asking them to argue in bad faith, that doesn't seem to be something we want to foster honestly.
The first prompt requires the reader to critically analyze the book, by first requiring them to give it a charitable interpretation.
It is said that you cannot disagree with someone if you're unable to explain their position yourself in a clear and definitive manner. Obviously, what are you disagreeing with if you don't even understand what's the ideas behind the thing you disagree with.
That's what the first prompt would be about teaching you, to be able to understand other people's ideas and concepts, to look past your initial judgements and bias, give it a charitable interpretation, demonstrate you understood all this by summarizing the idea in a 4 page essay of your own, with supporting references to tie it back to the source, showing the source does in fact argue for these itself.
Once you can do that, you have gained the right to go on with your own disagreement and write that essay, which would be your second prompt. Though honestly, your second prompt seems to be geared more towards discussing the entertainment aspect of the book, and not the ideas and concepts it contains, so again it's not that much about critical thinking, because critically there's little to argue about a "I prefer the color red over blue."
Personally I think you were trying to get at something else, maybe your point was just, come up with assignments students enjoy and can have fun with?
I think this is always true, but some things are just boring to some students, maybe you just don't enjoy reading, writing or even critical thinking, or any of that stuff. I don't know if there's much you can do in that situation. Maybe the solution is more fluid classes, let people move at their own pace, pick their own areas of interests, even if that's directly going to a trade, skipping on literature entirely, etc.