TIME Magazine (July 14, 1930): Thirteen Men is not a detective story, for the murders are all committed and solved in the first chapter. The rest of the book takes up the life-story of each of the twelve jurors in the murder trial, starting with each man's birth and ending with his opening the mailed summons for jury duty.
Can't rate this book, because I didn't (technically*) finish it.
What I did read was interesting, and decently written. What it is, is telling the different stories of 13 men, a killer and the 12 men who are called as jurors in his trial, showing how each got to where they were and how they arrived at the decision(s) they did. But other than the connection at the end (that they were all involved in the trial), there was no thread to tie their various life-stories together. You'd get interested in one character, and jump to another (who you may not have liked so well).
Interesting idea for the author to work on, but not so interesting to read.
* - I read the first few chapters, got bored and read the final chapter. Then, knowing the ending, I didn't care enough to go back and read it through. (I find myself doing that a lot with Romance-with-a-capital-R books.)