First, Volodymyr Ishchenko in Eurozine:
[T]he open letter signed by established academics, many of whom are mainly politically progressive, ignores the extent of far-right involvement in the Ukrainian protests. One of the major forces at Euromaidan is the far-right xenophobic party “Svoboda” (“Freedom”). They are dominant among the volunteering guards of the protest camp and are the vanguard of the most radical street actions, such as the occupation of the administrative buildings in central Kyiv. Before 2004, “Svoboda” was known as the Social-National Party of Ukraine and used the Nazi “Wolfsangel” symbol. The party leader Oleh Tiahnybok is still known for his anti-Semitic speech. Even after re-branding, Svoboda has been seeking cooperation with neo-Nazi and neo-fascist European parties such as the NDP in Germany and Forza nuova in Italy. Its rank-and-file militants are frequently involved in street violence and hate crimes against migrants and political opponents.
At Euromaidan, particularly, far-right attackers assaulted a left-wing student group attempting to bring social-economic and gender equality issues to the protest. Several days later, a far-right mob beat and seriously injured two trade union activists, accusing them of being “communists”. Slogans previously connected with far-right subculture, such as “Glory to Ukraine! Glory to the heroes!”, “Glory to the nation! Death to enemies!”, “Ukraine above all!” (an adaptation of Deutschland über alles) have now become mainstream among the protestors.
More here. Volodymyr Kulyk responds:
In his blinding opposition to both nationalism and capitalism, Ishchenko lumps together two very different matters: the role of rightwing radicals in Euromaidan and the role of these protests in Ukraine's choice of future. He is right that the radical nationalists do not share the protests' original goal of bringing Ukraine closer to the European Union and harm the democratic movement with their divisive slogans and their attacks on ideological opponents within the movement. However, he is wrong in arguing that such slogans and attacks invalidate the protests' value as a manifestation of the democratic and European aspirations of the Ukrainian people.
Although radical nationalists such as the Svoboda (Freedom) party and the less well-known organization called Rightwing Sector do not by any means constitute the majority of protesters, they are indeed rather prominent due to their vocal and visually striking behaviour.
More here. Also see this piece by Alex Motyl.