The problem is that if you didn't read the manga you won't understand the majority. Simply because they skipped so much stuff that you cannot possibly understand how they came to this situation. You won't have the background where it explains the story of some characters like Miza Kusakari a.k.a. "Three blades" or the past of Karao Saeki a.k.a. "Torso". They don't even show how some characters got to where they are.
In the end, I wouldn't recommend watching this anime excepted if you did read the manga and you just want to watch an animated version of what you read.
