You know how Bungie made games before Halo? One of them was called Pathways Into Darkness and it's just been given some love (i.e. remade) and is available from the Mac Store FOR FREE.
"In August of 1993, Bungie Software released Pathways into Darkness the most advanced and ground breaking First Person Shooter for the Macintosh.
The game broke new ground combining Adventure gameplay with the new First Person Shooter game that was just emerging onto the scene. As time passed, the Macintosh hardware and software changed and the game Pathways into Darkness was no longer playable on a modern computer… Until Now.
Painstakingly recreated and updated for OS X, Pathways into Darkness is now free and available for ancient grizzled fans and newcomers to the series.
Sixty-four million years ago, a large extra-terrestrial object struck the Earth in what would later be called the Yucatan Peninsula, in southeastern Mexico. The dust and rock thrown up by the resulting explosion caused enormous climactic changes in the ensuing years, and many of the Earth's species became extinct during the long winter that followed...."
Learn more about this game at the Bungie.org site