I'd be inclined to think that the ghast prob has long gangly limbs like a pale skinny 4 block tall giant corpse, and it shambles towards you and breaks blocks in its way (to make hell relatively un-inhabitable)
OSHI. If this thing is like the weeping angel, we are all ****ed. Say goodbye now. On a brighter note, say hello to people who want a good challenge and a scare. This may well be Notch's way of.. improving the community.