This is the story of two not-good people getting involved in a plot being pushed along by a bunch of other crappy people. Like, full disclosure, none of the adults in this book are good people. But that might actually be one of the things I enjoyed about it, the fact that these people could all very easily be categorized as villains depending on the story you're reading.
Note: Like many other reviewers, it's going to be difficult for me not to compare the book and the show here as I was watching and reading this story concurrently.
One of the biggest things that initially turned me away from this novel was that I had read a review which said this was a redemption story for Zhou Zishu, which I didn't think he was particularly redeemable after what happened Lord Seventh. Thankfully, it didn't give me that vibe. Could've been the translation but I never actually felt like Zhou Zishu was seeking redemption or really, even genuinely sorry about what he did. He felt it was necessary and his only real regret in the matter was how it impacted his younger martial brother. He is MUCH less soft in the book than he is in the show, but I like him more here.
Of course, Wen Kexing was probably my favorite, just in terms of pure shamelessness, and I liked the way he and Zhou Zishu played off each other. While the show did a LOT to expand on the plot within this book, making it much meatier and the side characters less one-note, I think it did do a bit of a disservice to Wen Kexing. In order to make Zhou Zishu look better, Wen Kexing had to look like he was a step behind some of the events in the show or was making missteps, whereas for the most part, book!Wen Kexing is definitely ahead of the game with everyone else.

Part of that might be because book!Wen Kexing actually knows who one of the ultimate villains of the story is before the start, whereas show!Wen Kexing misidentifies that person (so Zhou Zishu can figure it out first).

Also, I really hated the duplicate glaze armor bit in the show because the consequences of that extended much further than Wen Kexing intended and I feel like book!Wen Kexing wasn't that stupid. This isn't to say that Wen Kexing was a better person in the book. Only that his revenge plot definitely felt more focused on the people who'd actually wronged him, rather than lashing out at anyone and everyone.
YMMV on whether you find the plot insufficient. I personally liked the pace it moved at and the tighter focus, It didn't feel like it was being dragged out or becoming cumbersome like I did with the show, but it definitely doesn't take the time to expand on any of the characters except the main 3. There were a couple of scenes that hit me a lot harder in the book than in show

the constant push and pull of Wen Kexing and Zhou Zishu being friends or breaking up in the show made the scene when Wen Kexing found out the truth about Zhou Zishu dying so much less... impactful. They've already split up because of differences in opinions like six times at this point. What's one more? Whereas in the book, that's the first time that Wen Kexing tries to break away from Zhou Zishu (albeit immensely unsuccessfully) and I felt the heartbreak of that fissure a lot more strongly.

 Overall I found it an interesting story about two villains fighting against other villains in order to have their own good ending and somewhat of an exploration of "do the ends justify the means" at least where Wen Kexing is concerned. I'd definitely recommend it.