Anna Anthropy, creator of such relentlessly anticommercial titles as Mighty Jill Off and Tombed decides to sell out by creating a commercial Flash title for Newsgrounds in order to raise the bucks to move to the Left Coast. We can only wish for her further commercial degradation, since When Pigs Fly is a, I was about to say hoot, but let's settle for 'squeal of delight.'
As indicated by a quick cut scene, you are a pig who has fallen down a hole. You wish for wings, and get them -- but they're large and feathery, and the hole is small, and if you try to leave via the hole you fell down, the feathers fall off and you plummet with a squeal (or rather, 'restart from last checkpoint'). The rest of the game is a platformer, but one with an unusual control scheme; you cannot walk, only fly, and bump against almost anything and it's a plunge into the abyss for you (or rather, of course, 'restart from last checkpoint'). Maintaining height means tapping the space bar, and left and right arrow keys impart velocity that can only be counteracted with the reverse key tap, and in general manipulating the controls is non-trivial, even for those weaned on Super Mario and Sonic.
But the combination of fiendish level design, cute avatars, piercing piggy squeals, and sheer game design chutzpah carries the game. I suppose we'll see what Newgrounds's gormless audience makes of this, but at least it's not totally alien to their expectations, and we can hope for the best.