There were a few overdramatized items which viewers should look into to get the full understanding of Chernobyl (e.g. an actual dr from one of the hospitals that treated radiated victims discusses the burns and such on the victims)...
However...none of it takes away from the powerful story...and the realization of the depth of Soviet secrecy...
The non-Russian actors didn't bother me (why can't the best person get the job? Why do we have to put qualifiers on it? It is called 'acting' after all)...the leads were fantastic (of course - world class actors after all)...
A definite watch...and then look further into it to fill in what the drama doesn't cover.