Anders Åslund wrote an interesting piece on that question, published in 2002:
For ten years Ukraine was one of the sickest economies in the former Soviet Union. By 1999 most observers had decided that Ukraine displayed all the symptoms of economic malaise. It was hopelessly corrupt, market reforms were generally tardy and unfinished, the budget deficit was larger than the available financing, non-payments and arrears were rife. It is, therefore, all the more surprising that this country is currently experiencing an extraordinary economic surge, with industrial and agricultural production skyrocketing. Even if the present economic situation doesn’t last it is already remarkable and requires serious study. The purpose of this paper is to provide a quantitative analysis of Ukraine’s sudden economic growth and strong recovery. It begins by looking at common explanations of economic growth that have not proven relevant, discusses what concrete economic policy measures appear to have contributed to the generation of growth and ends by scrutinising how this was politically feasible. A proper understanding of Ukraine’s situation should help towards an understanding of post-Soviet transformation and offer clues about how to reform other countries.
For a more complete picture, I refer you also to his contrasting 2000 essay “Why has Ukraine Failed to Achieve Economic Growth?” Circa 2014, another piece or two could be penned on this topic.
Åslund has much more on Ukraine here, including this 2009 book. For a while now he has been predicting the end of Yanukovych, for instance in this piece. In any case he is the most prominent economist who writes regularly on Ukraine.