I've always been disappointed in the lack of recognition Dream Quest of Unknown Kadath gets. Several years ago, I read all of Lovecraft's works in a stretch, and while I enjoyed them all, Dream Quest really stood about. By the end my heart was racing and I was reading as fast as I could to find out what happened next. It's very rare for me to have any reaction to a story beyond the pleasure of reading or the appreciation of good prose.
But Dream Quest is consistently absent from lists of favorites or of Lovecraft's best writings. Maybe I just have bad taste. :) To be fair, it is a little different in theme than Lovecraft's later writings: less scientific horror and more fantastical horror.