The reason why I am asking this is coz it is very surprising to see Academy chose such a genre/popular movie as Best Picture
Is the reason-
1) Becoz it was so damn good, it's genre did not matter 2) Competition that year was not great 3) Due to the star power (Jack, Matt, Dicap,...) 4) It became a cult that time, and Academy had to go with the popularity 5) OP is wrong and such movies do get awarded Best picture (Please give examples)
What genre are you talking about? There have been other "organized crime" "gangster" movies that won. Godfather, Godfather II for example. There have been other "popular" movies that won. Gladiator, Lord of the Rings, Titanic for example.
It had great acting, directing, and writing. That's all subjective of course. Although the competition wasn't the greatest that I have seen - it certainly wasn't a runaway. There were some great movies nominated. The star power you mention is based on their great acting careers - at least for many of the lead actors.
So more to the point - yes I believe the Academy does award similar movies (by similar I mean movies with great acting, directing, and writing).
The Academy just sort of collectively decided to finally give Scorsese a sweeping win, because he had lost so many times for other, better films. For years, the press had been lamenting about how overdue he was for an Oscar, so they decided to give it to him.
It's the same reason Denzel Washington won Best Actor for 'Training Day', even though that wasn't really an Oscar worthy role. Denzel had already lost for so many other, better performances that were Oscar worthy, the Academy decided that it was just his time for the big win, finally.
It's probably going to happen very soon with Leo DiCaprio, too. Maybe this year for 'The Revenant', maybe not, but definitely sometime soon. The constant articles talking about how overdue he is are eventually going to get the Academy to give him the Oscar.
The Departed is a crime thriller though, as oppose to a crime drama. The genre is different compared to The Godfather, in the sense that it is a cat and mouse thriller, which the Oscars hardly ever consider.