There's Socialism Betrayed: Behind the Collapse of the Soviet Union that despite the sensationalist title is a pretty dry overview of the conditions and policies of the USSR from the 50s on, with most of its focus being on the mid to late 1980s. Its take on Gorbachev seems to essentially be that he was a likable, skilled bureaucrat who was good at enacting other people's policies but who was very much not cut out for leadership and who relied heavily on others to actually set policy directions for him.