When the two primary things discussed about a movie are the acting and the editing technique, that raises a red flag for me. Fine acting is great, but it doesn't make a movie. A solid story, characterization, a compelling point do that. This movie lacks pretty much all of that. You've read by now (I didn't actually know this when I rented it) that the movie is told seemingly at random throughout some unknowable period of time in the characters' lives by cutting back and forth from the past to the present. There is never any frame of reference for the viewer to try and determine when events are taking place, so when Watts' character talks about months having passed, it may as well have been a few days for all we know. Beyond the incapability of following the story this presents, it seems like the writer sticking his tongue out, as we form a conclusion about a scene we just saw just so 30 minutes later we see the preceding chronological scene and get the pleasure of thinking, "Oh, I was way off! Good job writer man!".
Sean Penn's character has no background, and attempts at showing one are almost irrelevant. Del Toro is rightfully acclaimed for his work, but his character exhibits something I find more prevalent these days: a character in a movie acting like a character in a movie, rather than a person. Naomi Watts goes full bore, and it's effective, but her motivations are also highly suspect, except that they advance the story as it was initially imagined. Having characters perform actions because it works within your story framework is poor writing. Let them dictate where the story goes, so that I care about any of them. As it stands, the only one I connected to was the ex-convict who has a heart of gold but should probably pawn it for all the good it does him.
I don't understand reviews that focus on the powerful human emotions on display, because without a story to back them up, it's just fluff. The ending, by the way, comes out of nowhere and tries to establish some sort of deep, meaningful conclusion, but doesn't seem to belong at all.