Papa Jazz has such a cool, mellow atmosphere. It's a small shop, but it utilizes every bit of space that it can--it crams hundreds of records, VCDs, DVDs, and CDs into a space that's only a bit larger than a breadbox. The cramped space is further compounded by the large throngs of people who shop there.
Their jazz record collection is bar none for Columbia. They sell a wide variety of CDs, too. I've bought some Chinese VCDs there before for relatively cheap--they were bootleg, of course, but still high quality. You can sell your old CDs here for a bit of extra pocket money.
Their world music collection is OK. Their used CDs are priced reasonably, and you can occasionally find some rare artists. My gripe: Papa Jazz really doesn't have that good of an electronica record collection. Woe.
Regardless, this place is very, very chill. Recommended, daddio.
PROS: Huge music collection. Good deals on the occasional rare find. Great staff.
CONS: Lackluster electronica record selection.