Ghost of Tsushima did get good reviews when it launched early this summer, although the consensus seems to be that it wasn't quite the same master piece as many other Sony games released this generation. But, this does not seem to have had any negative impact on the overall sales.
In a new article in the NY Times, it is revealed that it has in fact sold 5 million copies since it was launched in July. This is of course very impressive and hopefully means we'll get to see more from this universe in the future.