The Death of Stalin
While with minor story altering this could have been the perfect framework for a Tarantino movie (not to mention this feels like Russian Reservior Dogs), Armando Iannucci was the best man for the job with the witty tone they aimed for.
The biggest flaws I found were the two tones of polictal satire and the beginning scenes in Stalin's Russia pre-death clashing dramatically, the scenes of concert and the soviet army murdering civilians intercutting made for a tough time of picking when to laugh in the theatre. Thankfully this was no longer an issue once Stalin's sadistic methods were out of the picture. I'm not sure how I stand currently on the decision for all the actors to use their regular American and British accents, as it worked for some people (the northerner general and Steve Buscemi) but not for others (Jeffery Tambor and whoever played Stalin at the start), especially when characters call eachother 'comrade'.
I recommend knowing as little as possible before seeing this movie, as someone who knows next to nothing about Russian politics I therefore had no expectation to where the story would go. Excluding the first sequence none of the comedy scenes fell flat and the rest of the theatre laughed along too.