This probably has something to do with your network setup. I've been able to get the lag down sufficiently that some games are playable, though I'd never recommend playing a twitch-based FPS over Airplay.

For me what really made a difference was to ensure that only the laptop was connected to my network via wifi. My Apple TV is connected using ethernet. Before I made that change, I experienced significant lag, but now the lag is perceptible but pretty low.

YMMV, of course.