The Departed: Just a Fun Ride or Tightly Plotted? (Spoilers)

We went to see The Departed last night. I'm trying to figure out if I should try to figure it out or if, like "Snakes on a Plane," verisimilitude was not it's highest goal.

First, though, I have to say how gratifying it is to hear actual Boston accents (Matt Damon and Mark Wahlberg). What you hear 99% of the time from actors is this weird Hollywood concept of what a Boston accent sounds like; it's vanishingly rare to hear an actual accent. Damon, in particular, can sound like he never trained himself out of it.

Okay, spoilers hereafter...

My biggest question is simple: What was the basis of Costello's relationship with the FBI?

If he was protected by primarily honest Feds, then they must have been getting something out of it. But Costello only gave them underlings and people "who were going down anyway." The movie definitely made it seem that Costello was the top of the food chain, so the idea of him being a resource to get to another level of criminal doesn't really make sense dramatically. If, in fact, that was the idea, the Chinese chip smuggler situation would have gone down differently: if that was all a charade perpetrated by Costello and Ellerby (Alex Baldwin), either the Chinese would get away scot-free but compromised (not get busted at the border "with lightbulbs or something") or they would have been picked up that night in a way that let Costello escape (by the Coast Guard, say).

So the hypothesis that Costello was working for the Feds seems weak.

If Costello was protected by primarily corrupt Feds, then he was never in real danger from Ellerby. In fact, I think this would necessarily imply that Ellerby / Baldwin was corrupt. Ellerby was in charge post-Queenan. If Ellerby was corrupt, Costello would not have been ambushed at the drug raid.

So the hypothesis that the Feds were working for Costello seems weak.

The plot points came fast and furious in the movie, so I may very well have missed something. Thoughts?

I'll offer 3:1 that Scorsese finally gets his "Best Director" Academy Award.