Hmm...
* Fast-paced 2D action with intertwined with a procedurally generated and endless world.
* Explore surreal landscapes and twisted interiors in an apocalyptic setting, finding supplies to augment your spellcasting or settlement along the way.
* Enhance your abilities and transfer your glyph from one person to the next, cultivating a community of warriors and explorers, or place all of your eggs into one basket and maximize the potential of a single character. Each time period offers survivors with different strengths.
* Three kinds of bats!

AVWW is not an easy game to define, I've noticed. In general games that are so non-linear are difficult to write synopsises for.
Something else noting how the game has evolved due to the interaction between developers and players. Always my favorite thing about your games, yet it's the hardest thing to convey to someone who isn't familiar with you guys. Too bad you can't just put "Seriously, we patched the game nearly every day. That's how awesome we are."