Peter Ericson’s review published on Letterboxd :
Can a film in which four people basically just talk and which takes place within a single apartment be funny? In this case, yes, definitely yes. Hilarious and occasionally poignant, "Carnage" soars to a level of comedy rarely reached by chamber dramas.
At 80 minutes, the movie is neither so long that it overstays its welcome nor so short that it becomes inconsequential. As the darkly comic narrative progresses, the intensity of the initially civilized discussion increases many times over, until the characters have regressed to child-like conflict behavior not unlike that of their sons, whose actions started the whole thing. The scene in which one of the characters “tosses her cookies” might not be particularly funny in and of itself, but the aftermath certainly is.
Roman Polanski’s direction (Polanski also co-wrote the screenplay with Yasmina Reza, who authored the play "God of Carnage", upon which the film is based) is restrained almost to the point of anonymity, never detracting the viewer’s attention from what really matters: the acting and the dialogue. Ah, the dialogue! It’s wonderful and very well written, with numerous great lines and plenty of wry humor.
The movie is nicely shot by director of photography Pawel Edelman, with its relatively warm visual tone standing in contrast to the prevailing cold mood of its characters. Alexandre Desplat’s minimalistic music has a not insignificant comic efficacy.
"Carnage" features marvelous performances by the four lead actors (actually, there are only a couple of other actors in the whole movie), three Oscar winners and one Oscar nominee. Jodie Foster is brilliant in the role of Penelope Longstreet. Kate Winslet is brilliant in the role of Nancy Cowan. Christoph Waltz is brilliant in the role of Alan Cowan. John C. Reilly is brilliant in the role of Michael Longstreet; I was positively surprised by the fact that I found him to be the thespian highlight here. The four actors hit all the right notes and carry the film superbly.