Just in time for Halloween, Valve Software has released Left 4 Dead Game of the Year Edition for the Macintosh. The game is regularly priced at $19.99 but costs $9.99. It’s available through Valve’s Steam download service.

[ad#Google Adsense 300×250 in story]Left 4 Dead Game of the Year Edition is the definitive version of the Valve’s original zombie-themed cooperative action game, in which you and a team of three others make your way through a landscape crawling with hordes of bloodthirsty zombies and vile, mutated monstrosities.

The game includes single player and co-op multiplayer elements, 20 maps, 10 weapons to choose from and four “movies” that set the tone. The game also incorporates matchmaking, achievements, stats and rankings. The recently-released expansion pack “The Sacrifice” is included.

Left 4 Dead Game of the Year Edition follows the Mac release of Left 4 Dead 2, which came out earlier this month.

System requirements call for Mac OS X 10.6.4 or later (Snow Leopard Graphics Update required); dual-core Intel processor running at 2GHz or faster; ATI Radeon 2400, Nvidia 8600M or better 3D graphics.