For my money, this opening image from the first Vampire Hunter D anime is the most powerfully succinct bit of world-building I've ever encountered. It does everything with very little. The ominous image of Castlevania-style castle paired with two blood-tinged moons screams Gothic, while the texts fills in the other important aspects of the setting: it takes place in the future, so get ready for incongruous technology; there are mutants and demons, so get ready for the monster mash; this is a world of darkness--and you know what that means.
All that in a single pairing of image and terse text. Brilliant.