The concept sounds like a joke, but it's actually a pretty great new gameplay mechanic. Instead of running from ghosts that move by their own volition, you're running from ghosts that you control — sort of. The creator explains:
Ever wondered how Pacman would be like with physics? No? Well, it's revolutionary. This mashup of "Not" and "Pacman" puts The Pac and the Ghosts in a in a Pacworld cage, at mercy of gravity and the level's shape, controlled solely by you. Ghosts still don't like you very much, so you should be careful to make Pacman avoid them.
You can download the game for free for Mac, Windows and Linux.