Movie probably deserves a 3 compared to other MCU movies; but Black Widow was always my favorite MCU character; so 4 stars it is.
Two things stood out to me. The first was that the first 1/2 or maybe even 2/3rds of the movie I felt were very slow/calm/tame/whatever for a MCU movie. The second was the ending. It feels like there is at least a (lengthy) scene 'missing'.
Overall, *I* really liked the movie and wish it had come out a few years earlier.