I have not been waiting the full fifteen years for this book -- I originally read Shades of Grey in about 2016 -- but I have been waiting very nearly a decade for it.  And when I discovered it had finally been published, I was completely over the moon!  And, before starting it, I decided to reread Shades of Grey. 

This might have been a mistake.  Compared to Shades of Grey, Red Side Story lacks something.  The writing feels a little forced in places.  There are a few pretty glaring editting mistakes (such as a lack of paragraph breaks between dialogue, which means figuring out that the speaker has changed and making sense of a scene takes a couple of rereads because it doesn't make sense otherwise), and then a few continuity errors and retcons that really frustrated me for the first half of this book.

I'm pretty sure if I hadn't finished Shades of Grey and jumped immediately into this one, this would have been much closer to a 5* read. 

Anyway, it's still great!  Still funny -- though not as funny, IMHO, as Shades of Grey.  Still whip-quick and clever. Still very intriguing and imaginative.   Just, you know, maybe not as good as it's predecessor. 

I very much hope that I don't have to wait another fifteen years for the final book in this trilogy, because I need it.