You will be hard-pressed to find a better English-language history of the past 150 years in Vilnius and in Volhynia/Galicia. Snyder goes into great detail about the history and ironies of Polish, Lithuanian and Ukrainian nationalism (Belarussian history and nationalism, described as a "national failure" by Snyder, gets shorter shrift). The modern history of these until-recently contested regions is quite complicated and arouses great passions from Poles/Lithuanians and Poles/Ukrainians to this day. Snyder does an excellent job of trying to approach the history here as something fresh, rather than try to amalgamate different competing national mythologies.
A warning: this is not a comprehensive history of the region, and is not even really a comprehensive history of modern Polish, Lithuanian and Ukrainian nationalism. A great many events, places and people are mentioned in passing, and if you do not already have a firm grounding in East European history you can easily get lost as the tides of history swirl by. The book is best understood as having, at its heart, a history of the Vilnius guberniya and a history of the Volhynia guberniya and Galician Koenigreich from about 1900 to about 1950. The chapters on Volhynia during the Second World War are at once both the most harrowing and also the most illustrative as to how individuals and groups were able to switch back and forth between ideologies and how persecutions and atrocities were able to build one on top of another. This goes a much longer way than many other recent histories in explaining just how genocide and ethnic cleansing was able to occur in Europe in the 20th century.
The last third of the book, dealing with Polish foreign policy, is the weakest (and the most poorly-edited). It felt a bit like a thesis paper spun out into 100 pages of a book: the same argument was largely made over and over again as to how Polish foreign policy post 1945 was able to be shaped by emigres, and how this foreign policy achieved peace in Eastern Europe post 1989. Honestly, this had little to do with the rest of the book, except as an epilogue, and would probably have been better handled in a separate book. It felt a little too idealistic, a little to Poland-centric (and largely focused on the ideas of a few elite, at that) and definitely controversial. For all of Snyder's arguments, no explanation is really ultimately given for why Poland was able to adopt such a forward-looking foreign policy, especially after all the conflicts and persecutions that he just finished documenting a few chapters earlier.
In any event, the book is a good read, covers a good breath of history in a wide area, and will be a welcome supplement to anyone interested in the region's history.