There's a major difference between K.L. Saigal, Dilip Kumar, Shahrukh Khan and Abhay Deol's Devdas. The first three films were faithful to Sarat Chandra's legendary novella, while Anurag Kashyap's deviant take on Devdas is contemporary and in the process, differs from the original work.
In Kashyap's Dev D, Dev is into drugs and vodka. Paro sends her nude pic to Dev via email and later, wants Dev to have sex with her in the fields. Chanda, a hooker, indulges in phone sex mainly. Clearly, Kashyap's Dev, Paro and Chanda are audacious and rebellious.
There's no harm if you pick up an enticing story and tell it your way, but Kashyap goes a bit too far, crosses all limits and tends to get abstract once again. And that's the reason for Dev D's downfall.