Kallistos Ware is a renowned bishop of the Orthodox Church and a stellar writer and scholar who has done great work in the field of Orthodox apologetics. I recently purchased a used volume of The Orthodox Church and read it with great interest. One thing that Catholics should know, is that while he is not virulently anti-Catholic like some Orthodox I have come across, his writing presents a solid and unapologetic Orthodox POV, and that sometimes means defending his own tenets of ecclesiology, theology and history that run counter to Roman Catholic sensibilities. That being said, any well-formed Catholic should be greatly edified by his perspectives, and his books are a gem to find in any respectable library.