Brian Sweeney’s review published on Letterboxd :
Early on in Manchester by the Sea, there's a flashback where Joe Chandler (Kyle Chandler) learns that he has a congestive heart failure that will someday kill him. His doctor mentions that it's "not a good disease," to which he jokingly replies, "what's a good disease?" and she says, "poison ivy." This joke clearly makes Joe smile, but it causes his wife (Gretchen Mol) to get angry and storm out of the hospital.
It's rare that a film could be a contender for both funniest and saddest movie of the year, but Manchester by the Sea understands the inextricable, and often inexplicable, link between grief and humor. Movies can be comedies or tear-jerkers, but in reality, moments that make us cry come right after those that make us laugh. Something that keeps coming up about this film is how it's the most "human" film of the year, and this is a big part of why.
Another big part of that is Lonergan's keen understanding of how the baggage we bring to difficult conversations manifests itself in stammering, awkwardness, and discomfort, not in huge dramatic statements. In lesser hands, Manchester by the Sea would have been melodramatic and cliche, but instead it realizes that tragedy, guilt, and grief are often endured below the surface.