This book blew my mind. Reading it was interesting, but the thoughts that it provoked were amazing - as he puts it (which seems to be the best way) it opened up an entirely new avenue of experience. Huxley's enormously wide breadth of knowledge of music, art and literature means he makes references to many works outside of mine (and I suspect most people's), and I didn't always agree with his theories, but these are tiny quibbles about a brilliant book that should be, IMHO, read by everyone.
The Doors of Perception is Huxley's account of an afternoon on which he sat down and, in a controlled experimental situation, took 0.4g of mescalin (a drug not dissimilar to lysergic acid). Heaven and Hell is his later reflections and the paths down which his thoughts went following this experience.
I generally read books simply for entertainment - this one gave me another perspective with which to look many things and left a strong, permanent and very postive effect in me.