If recent reports pertaining to "Dhoom 3" and Aamir's character are to be believed then Aamir's playing negative character is not the sole USP of the movie, rather it's the double role of Mr Perfectionist which is the surprise element.
Buzz even suggests that this surprising twist is something pertaining to "mentally-sick-twin-brother" kind of phenomena, and will come somewhere around the climax of the movie.
The movie also features Katrina Kaif, Abhishek Bachchan and Uday Chopra.
So all you die hard fans of Dhoom and Aamir, be prepared for "two-much" of Aamir and thrill.