Is It Right to Write a Review, When You Haven't Finished Reading the Book?

When I was in University, I volunteered for the Toronto International Film Festival. I thought it would be an exciting opportunity to see the festival firsthand, maybe see some celebs and get some insider information into the world of filmmaking. Mostly, however, it was pretty boring. My feet hurt, I was hungry, and everything felt pretty disorganized. 

I elected to volunteer at the Press & Industry screenings, thinking it would be cool to see various press people go and watch movies they were then going to review. However, I began to notice that maybe 20 minutes into the movie, the press would leave. They wouldn't stay for the entirety of the screening and I was told that this was common practice; they had what they needed, and they could base their review off of the very little they had seen.

That brings me to now. I was planning on writing a book review about the incredible Smoke by Dan Vyleta, but I'm only about halfway through. I thought I could tease out what the book was about and maybe hint at a twist ending (of course, I have no idea if one exists in this book), but I figured it wasn't fair to the author and to myself to write a review based on an unfinished reading. I don't have enough information to make a solid conclusion. I want to know if there's a twist ending that I can hint at. So this review will have to wait until I have completed and read each word of Smoke so it can get the full respect and review it deserves.