It was critical of the USSR. In the first episode, just before cutting the phone lines to the city, the mayor of Pripyat gives a hilarious "bad guy" speech about the need to do evil in the name of Lenin. And in the last episode, Legasov extols on the superiority of the West in a grand speech that was entirely fictionalized. At several points it also depicts Soviet people as slaves operating under the constant threat of execution (e.g. Legasov on the helicopter and the miners).

Well the reactor was very critical