I really don't know what else I'd suggest as an overview. Beyond that I think it's really a matter of reading and absorbing the texts themselves. Philosophy, of course, has fuzzy borders, too. Are you also interested in political theory based on philosophy? What about religious philosophy? Many overviews are going to jump straight from the Greeks to Descartes and Spinoza because they will consider all medieval philosophy to be "worthless" given that it's framed in a religious context, yet scholasticism was an extension of Greek philosophy, and the Reformation essentially started when the scholastic notions were challenged.