The M5 is a magnificent car. I don't know why it has been so maligned in the press. But I never listen to magazine reviews as part of their income comes directly from the manufacturers in terms of advertising, etc, etc.
I have either owned or have had extensive seat time in all the cars that compete in the M5 segment and IMPO the M5 lacks for nothing. Ultimately, that's why I bought the M5. However, I will say BMW must improve on their customer service. But that's a topic for another thread