Conquest is definitely NOT unbiased. Although The Great Terror is one of the books to read to be familiar with the historiography, it is not a book to read without a good grounding in Soviet history.

The anthology Stalinism: New Directions is a very good starting point. Part of Routledge's "New Directions" series, the anthology has what were at the time (2000) some of the most important post-1991 articles in Stalinist scholarship, and many of the contributors to the anthology are now the doyens of Stalinist studies in the academy. Stalin has received two rather recent, excellent biographies: Stephen Kotkin's Stalin: the Paradoxes of Power and Oleg V. Khlevniuk's Stalin: New Biography of a Dictator. Kotkin's work is the first of a planned three-volume biography of the dictator, but like Khlevniuk, benefits from access to the archives and synthesizes a great deal of secondary literature on the topic. Sheila Fitzpatrick's On Stalin's Team is a good and accessible examination of the group dynamics of Stalin's team. Fitzpatrick's voluminous corpus of work (eg Everyday Stalinism, Tear Off the Masks, Stalin's Peasants, etc.) are essential reading, as is her 2015 article "Impact of the Opening of Soviet Archives on Western Scholarship on Soviet Social History" in Russian Review. Three recent books have put the Purges into sharper relief and use archival sources and new access to the former USSR to their benefit. Inventing the Enemy: Denunciation and Terror in Stalin’s Russia by Wendy Goldman covers the experience of the Terror from the bottom-up and the ripple effect denunciation had and the blurring of the line between victim and perpetrator in this charged climate. Two of the vexing questions of the Terror is how did it seemingly come from nowhere and why did it destroy the Red Army; Peter Whitewood''s The Red Army and the Great Terror: Stalin's Purge of the Soviet Military answers both these questions in an accessible and quite original monograph. Paul Hagenloh's Stalin's Police: Public Order and Mass Repression in the USSR, 1926–1941, like Whitewood, also examines the long-term processes for police terror and organization that were latent triggers in the Soviet system. Finally, Karl Schlögel's Moscow, 1937 is one of those books that manages to convey the feel of an era and how that particular year managed to both enfold both terror and hope for many Muscovites in that fateful year.