Just watched The Departed (starring Matt Damon, Leo Di Caprio, and Jack Nicholson). Compared to Infernal Affair (IA), this film is losing everything except good and famous casts. You should watch IA if you said The Departed is an Oscar condender. IA is really an efficient storytelling film, keep every scene worth telling, and natural film-ending.
Comparing an adaptation film may not be unfair for some people, but I have to put some points in Tony Leung's performance, that you couldn't find that quality in Leonardo Di Caprio.