If you need a guidebook to visit Bulgaria, this is not the book you should buy. Major mistakes in history, cities descriptions and biased commentaries make this guide useless for people who travel the first time to the country. Travelers will learn that there is an impressive Roman castle in Vidin, or search for prehistoric constructions around the Belogradchik rocks. Tough task, since the Vidin Castle is Medieval and the Belogradchick rocks don't have any prehistoric construction preserved. You will learn that by October all Black Sea resorts have closed, which is totally false. There are endless possibilities to stay on the Black Sea coast during October, for less money and huge discounts, and many of the hotels (all 4 and 5 star hotels, for example) are open year around. In Nessebar, UNESCO World Heritage Site, you will search for Roman ruins (again, is everything that Lonely Planet see in Bulgaria "Roman"?), where surrounded by Byzantine Churches and medieval Revival architecture.
Biased and false commentaries such as "youthful maritime cockiness of Varna" are abundant. (Varna is one of the most elegant cities on the Black Sea Coast, often compared to Barcelona or Lisbon, plus it hosts the oldest gold of the world, recently exhibited in NYC. There is nothing "cocky" about the city - an adjective better used for Burgas, for example).
The examples of lack of accuracy are endless. My advice: go with Eyewithness Guide or any other guidebook.