It was a good movie. The ending was only mediocre.
There are certain films where the protaganists can die at the end, and, although sad, the audience can pleased with the ending (Spartacus, Gladiator, Sin City, for example). This is not the case with The Departed. after so much tension and anxiety about seeing if Cartigan were goign to be cuaght or not, and after his seeming triumph, it could not be considered 'fair' to have him killed so abruptly and unfortunately.
I did, however, like the very end, where Dingham finishes off Sullivan . I liked the Dingham character quite a bit.
I also liked the Sullivan character off the bat, due largely to his sarcastic and rude style (reminds me of someone I know very well...). His character seems to take a complete change, however, about the time he is assigned the SIU with the new crew. After this point, his character changes, and the audience is led to dislike him.
Over all, I would recommend this film. It has an abundance of foul language, though, so don't see it with your grandmother.