An Enquiry Concerning Human Understanding
Was vv excited to read this after Descartes, specifically because Hume was a skeptic, and I wanted to read about the human experience being built up from the senses without God being used to explain away any genuinely provoking questions.
I enjoyed his critique of traditional metaphysics, and his distinction between the "easy" philosophy that appeals to human emotion, and "hard" philosophy, which is more abstract and seeks to map human nature. I thought his idea that the principle of induction has no logical justification was interesting, although I don't necessarily agree (you can read my thoughts on this here). He goes on to talk about the limits of reasoning, and how cause and effect doesn't exist the way we understand it.
Didn't end up enjoying as much as I thought I would, especially because Descartes' Meditations were written much more digestibly, but still a good read!