Let me start by saying it's not a bad fare at all. In fact you would only feel let down because you would keep comparing this film with the original. And that's bound to happen. For me even more so, because I saw the original and the duplicate on the same day.
Shahrukh tries his best, but fails to emulate Amitabh's suave, sophisticated panache. In fact his proclivity to overact consumes him. Shahrukh looks horrible as well - except the long shots. DON from the cold, calm, composed character is converted to a hyperactive, over-expressive and devilish character, which breaks the traditional mould of a DON. I don't mean to imply it is bad, but it just doesn't suit a DON. It suits more a BAD-MAN ala Gulshan Grover, with the hangover of BOND, James Bond.
About the handling of story, I am a disappointed with one of my favourite Directors - Farhan Akhtar. He has definitely not done justice to the story. In fact in some cases he hasn't explained what is happening in the story and a person who wouldn't have seen the old film would be lost. Farhan relies on the old fare completely. Yes, it is shot very stylishly but all characters except the DON are underplayed.
Priyanka Chopra and Arjun Rampal would feel let down because they would have expected a little more when they would have signed the film. MAIN HOON DON song and amazing AAJ KI RAAT, are 2 show stealers. The 2 re-mixes are strictly OK.
The problem with the old DON was that it was full of clichés (but that was the norm of the era) and the new DON is that it fails because it tries to make those clichés - real. Yes, it has to fall back on super-human and flamboyant stunts but that's understandable.