Just a random thought..
西游记: this is easy – RPG game with many bosses battles. The essence of the book is a group of 4 ppl going the West with many monsters on the road.
三国演义: this is easy – SLG strategy game (turn-based), or RTS game. The book is about a period of Chinese ancient history when three kingdoms fight each other.
水浒传: this can be gacha game like Genshin Impact. The book has 108 characters, each has unique backgrounds and skills.
红楼梦: this one is hard. What makes this book unique is its detailed depiction of lifestyle during Qing Dynasty. Maybe it’s metaverse game, or story-based romance game.
These 4 famous books each has its own appeal to a wide range of audience, which can reflect certain underlying demands. And these books’ popularity is proven over time.
Game developers need to constantly think about what “needs” they are catering to. Any thing that is popular for a long time must have served some pain points well.