Finally saw the movie (with my wife and son) in (indeed) glorious HD. What a brilliant movie!
I don't think it's fair to the Academy to say that Scorsese got the Oscar for the wrong movie in his career (and perhaps, some might disagree

), because Oscars aren't administered "vertically", in time, for your own work, but "horizontally", in a comparison with works of others during the same year.
Of course one can still disagree with a particular Oscar (

), but it's quite possible and all in the system that a brilliant movie could lose the Oscar to an even better one, while a slightly lesser movie of the same director wins in another year.
Anyway, I think this year's Oscars were rightfully granted to The Departed.
About some of the above critique: Jack's character was an FBI-informant indeed, but as he told Leo he only fed (pun intended) guys to them who were about to go down anyway. So he really provided them with serious looking information sometimes, from their point of view, but rather inconsequential from the mob's, or at least his own, view.
Also, I think Billy's death was in line with the story. Part of the message is about the way you get contaminated with the side you're in as a mole. Your hands
will get dirty, and your
may get corrupted when you're in the mob and you
may arrest some thugs or even kill one of the bosses if you're in the police.
There's no doubt, IMO, that Billy was willing and going to kill the guy who almost blew his cover. It only didn't happen because the man died on him first.
Note the tiny parallel: a "second" inactive mole in the gang (at least it's more than hinted at that the guy was indeed perhaps a police plant, although that may also have been a distraction only) saves him, and Billy was ready to kill
him, while later another "second" inactive mole (in the police team) indeed finished his life for an equivalent reason.
And in both cases the sleeping moles play a bit of a
deus ex machina.
This is a typical Scorsese movie indeed. Hardly any likeable characters (only some more "innocent" ones) and it keeps you thinking it over a lot afterwards.
And, once more, brilliant!
I think I will go and see this film a second time soon.
Cees