This is one of the historical questions which fascinates me. Unfortunately, the actual event happened when I was mostly interested in playing in the sandbox with my monster trucks, so I have no first-hand knowledge of the events and the lead-up to them. I asked some people in Russia about it, and most of them tell me they don't understand why or how it collapsed. I get the feeling that its collapse was a largely unexpected and shocking turn of events.
In spite of the gravity and drama of this event, I have been unable to find any well-informed, reliable, and at least not blatantly politically and ideologically motivated book or literature on the topic. Is there any book or source that provides a balance of theories, explanations, and points of view as to how and why the Soviet Union collapsed? I'm not a historian, so I have a hard time evaluating if a book is something that historians would take seriously, but that's what I want.
Thanks for sharing your knowledge and expertise in advance!
The Rise and Fall of Communism by Archie Brown is a really fantastic source Imo. I would definitely recommend it.
A couple of suggestions:
Archie Brown's The Gorbachev factor might give you a reasonable grounding in the political atmosphere and goings on leading into the collapse.
Stephen Kotkin's Armageddon Averted takes a more critical view of Gorbachev's role, reforms and exactly what it was that broke the system (and perhaps why the system failed to 'defend itself'). Also covers what came after.
Alexei Yurchak's Everything Was Forever Until It Was No More, particulatly the later chapters, explain the common mindsets of citizens in the USSR, how they could believe in the USSR... but also quickly understand it as irrelevant too. A bit different in approach generally, first chapter can be a bit heavy but stick with it.