Am presently reading a book about Gorbachev. Agree, not the easiest read but interesting.
Some people are great because of what they have done. Others are great because they did not do what they could have done. Gorbachev is the latter.
The Soviet Union ceased to exist as of 25 December 1991. Gorbachev was first and last President of the Soviet Union. He had control of the Soviet nuclear "football" until turning it over to Boris Yeltsin late on that Christmas Day afternoon. That turnover happened quickly and smoothly.
But things could have turned out much differently. Gorbachev could have said to himself, "Well if the Soviet Union is collapsing, may as well go out in a blaze of glory!", and "pushed the button". To his eternal credit, Mikhail Gorbachev did not press that button. I believe a Lenin or especially a Stalin would have done so in the same situation. Khruschchev, Brezhnev, Andropov, Chernenko - no, they wouldn't.
I grew up worrying about the prospect of atomic war with the Soviets, read my share of post-apocalyptic literature. Now that worry was gone. Better yet, I was happy to see that sword of Damocles removed from above the heads of my kids, 8 and 4 at the time. Many of you were born after Christmas 1991. You got to be born, live, grow up.
I'll be sad when Gorbachev passes away. Great because he did the right thing at the right time.