Well by the standards you've set this is positively modern, but I'd say my favorite 'old' book (indeed one of my favorite overall) has to be Far from the Madding Crowd by Thomas Hardy.
I love how bold the story felt playing with the idea of gender and power in the Victorian English countryside. It was also surprisingly sweet, and I hold the storm scene after Bathsheba's marriage to Troy in my hall of fame romantic hero moments.
The book is just pure comfort for me, like a blanket and a warm mug of cocoa by the fireplace. Bathsheba and Gabriel Oak were such good characters and i couldn't help but cheer them on, I just loved it.
I also just find it so interesting that Hardy, who is in my opinion, author of some of the most bleak and hopeless stuff out there, is responsible for such a tender tale.
I am not at all confident that anyone, least of all these two chuckleheads, are capable of adapting this series faithfully. IMO this is a story best kept to the page, at least for now.
I'm expecting original Dune (1984) levels bad.