This is my first by Steinbeck. I can see why he is renowned. I knew nothing about it going into the book but I found the beginning similar in feel to flowers for algernon (haven't actually read that one but my high school performed the play when I was a teen) 
I think it was best to go into it without any spoilers so I'm not going to put anything here. But I did cry after I finished it. 
Steinbeck is an incredible and compelling writer. 

I will note that I was very annoyed with the loud music played over the narration for the first 90sec of the audiobook. I couldn't really understand any of the first two minutes of listening. I also just wasn't a huge fan of the narrator. So I'm rating the book, not the audio itself, and would probably recommend finding a different audio recording or reading physical copy.