I found it quite accessible and have read it end to end twice. It's not a Russian heavy literature doorstop a la War & Peace, but an encyclopedic one-man survey of every aspect of the camps, roughly in chronological order: first the the history of labor camps in Russia, then the journey of a typical inmate (arrest, interrogation, trial, transit, arrival, life and death in the camps for prisoners and guards alike, freedom [1]), then the slow winding down of the system.

[1] In some sense, at least; see https://en.wikipedia.org/wiki/101st_kilometre