As far as I'm concerned The Departed is an excellent movie... Nicholson is simply extraordinary, he's got a gift for playing psychopaths (Shining ). DiCaprio was amazing too, and Damon, who I thought would be the weakest of the three, did pretty well.
Lucky number slevin was cool in my opinion.
Of course it's not realistic but I wasn't expecting a realistic movie.
But I admit I found the end a bit long, we didn't need that much explanation