I'm currently reading Alasdair MacIntyre's Three Rival Versions of Moral Enquiry (based on his Gifford Lectures)--which is a rather dry title for a book that looks at the fascinating history behind philosophy since Aquinas in the Middle Ages. It's become sort of a cliche, I know, about philosophy these days that, in stark contrast to the cumulative success of science in explaining the natural world, philosophy just seems to bat around the same questions without ever coming to acceptable answers. And worse, bats them around in arcane languages that no ordinary person would understand. (Just one of the reasons scientists love to make fun of it, and who can blame them?)
MacIntyre makes the point (among many others in an excellent read) that this paralysis was not the case for philosophy before Aquinas. That, in fact, you could read philosophy at the 'new' universities in the 13th century--as many did--as a progressive accumulation of wisdom from Socrates up to Aquinas, and that it was only with his passing, and the subsequent misunderstanding of his (dare I say it) holistic approach to wisdom, that philosophy has slowly disintegrated into multiple competing schools that can't even agree on the right questions anymore, let along what the answers to those questions might be.
Aquinas deliberately left his Summa open ended. He knew he built on the work of those that came before, and expected, or hoped that many would build on his work after. Instead, his work was almost immediately condemned and even when his work was revived in later decades and centuries, it was only in dissections, never as a whole, and too often it was never studied in the same spirit.
Anyway, this just scratches the surface of what MacIntyre is getting at. Not exactly beach reading, but if you want a challenge, and you find the history of philosophy less daunting than philosophy itself, I recommend it.
Update: Brandon over at Siris has been mulling over MacIntyre as well.