Apparently it's to do with the writing and direction. From what I could see from the reviews it covers the racism perfectly, Will Smith is good and Joel Edgerton is excellent, but there's no effort put into the side characters and the story gets lost and confused in poor writing. That said, the reviews aren't all bad. If you look on Metacritic there's a review that gives it 0/100 and says it's the worst thing ever created then there's a review that gives it 100/100 and says it's amazing. I'm still going to watch it and I wouldn't be surprised if I enjoy it.