Conquest pretty much wore his anti-Soviet and anti-Marxist bias on his sleeve when he was alive. Much of his original work such as The Harvest of Sorrow was pieced together when the Soviet Union was still existing, so his original source bases are often quite poor and themselves quite biased (the USSR was never terribly friendly to Western researchers, least of alll avowedly anti-communist ones like Conquest) Reading Conquest in 2017 is something of a chore, especially since there are much more sophisticated works on the Soviet Union that have been produced since 1991. The Years of Hunger: Soviet Agriculture, 1931–1933 by Davies and Wheatcroft, for instance, is a much more balanced and nuanced account of collectivization that Conquest's polemical tone. When Conquest did revisit his books post-1991, it was not to modify his thesis but to sharpen it. And there is a persistent undertone in post-91 Conquest that he wants the left in the West to abjure their alleged faith in communism and accept the worst aspects of the Soviet system. Naturally, Conquest along with Pipes have some currency both among the anticommunist crowd, but also among various Eastern European nationalists in which the very worst interpretation of Soviet actions fuels narratives of national martyrdom and post-Soviet rebirth.

My personal advice is that unless you're looking to familiarize yourself with the deeper historiography of the Soviet system, and Conquest is referenced a lot (albeit mostly in introductions and snarky dismissals in the footnotes), he really is not worth reading today. There are much better and more reliable secondary works on the the Stalinist period, almost to the point of saturation, and they present a much better picture of the Soviet system than Conquest. New generations of historians have pretty much superseded Conquest on all of the topics he pioneered. Conquest is an artifact of its era and really leads people wanting to learn about the Soviet system into a bunch of dead ends.

Suggestions for alternate sources: pretty much anything written by Sheila Fitzpatrick is good; Years of Hunger is dry, but much better on the famine; the anthology Stalinism: New Directions is an excellent introduction to the post-91 historiography; The Kirov Murder and Soviet History by Matthew Lenoe is a good counter to Conquest, who accepted the charge that Stalin murdered Kirov; Oleg Khlevnuik's works on the Terror and Stalin are good introductions; Lewis Siegelbaum's books and articles pioneered the "limping behemoth" genre of the historiography in which systematic incompetence more than terror undermined faith in the Soviet experiment; finally, to get a good sense of what it was like to live under Stalin, Karl Schlogel's Moscow 1937 is a rather breathtaking read despite being a doorstopper of a book.