The Departed is better than your average film but that is only because Martin Scorsese is better than your average director.

Rating: 7/10 (6 March 2016)

Strip away the glossy exterior of possibly questionable performances by an all-star cast with the direction of a stellar director and you are left with mordantly skewed dialogue from an unoriginal (adapted) script written by the infamous William Monahan who destroyed Ridley Scott's filmography with 'Kingdom of Heaven' (39% RT) and 'Body of Lies' (54% RT) a year or two after some of Scott's greats such as 'Gladiator' (76% RT) and 'Black Hawk Down' (76% RT). Spoiler Alert: His other movies he did the screenplay for: Mojave (2016) got 31% RT (Mark Wahlberg was in this one too). Edge of Darkness got 56% RT. The Gambler (also with Mark Wahlberg) got 46% RT. THESE ARE HIS TOP FILMS. Also I can see Wahlberg trying to get that Best Supporting Actor Oscar with his harlotry by working with Monahan seeing as The Departed got him a nomination for the Best Supporting Actor Oscar that year. If The Departed was written so well why then has Monahan shown that apart from a stolen script he cannot make a proper script? If the Departed was written so well then why has Scorcese refused to make The Departed 2 (Monahan had made a script that would involve bringing back the actors)? If The Departed had such a good script, with so many good actors, with such a large budget for its setting (half of it going to the actors), and Robert DeNiro being in 8 of Scorsese's films with most of them being classics why then did Robert DeNiro decide to decline the offer to star in the film and make another? These aren't conclusively damning questions but watching the movie itself conclusively damns the script...
Also, read the first paragraph of the reviews from the Top Critics of Rotten Tomatoes. Most of them praise Scorsese, the actors and how funny the movie is. Only a couple of the Top Critics praise the plot and screenplay. Only one praises Monahan. Also about 8 out of the 44 demonise the film itself.
Everyone was too eager since Casino (1995) to see another true Scorsesian movie and jumped on the bandwagon of this one thinking it was what they needed. In the past 10 years this has been a truer Scorsesian movie just not a great one. Also, swearing and profanity doesn't pass for a good script either. In fact you are more likely to use these tools when you don't have a good script.
P.S. % RT = Rotten Tomatoes critic ratings.