I concede that the acting was good, as all characters were believable. But isn't that the expectation with any decent movie?
There are a zillion movies with believable characters - what was special about this one that I couldn't just as easily find in another movie? I'll contrast it with another northeast fishing-town movie dealing with grief: In the Bedroom was a fantastic movie to me. Obviously, the climax was of a greater magnitude than Manchester by the Sea, but the performances were outstanding.