Valve is offering gamers the chance to download its entire 22 game back catalogue via Steam for $99 ($70).

The offer includes Valve's upcoming zombie shooter Left 4 Dead, which is released on Friday, November 21.

Valve: Complete Pack contains all of the Half-Life titles as well as the critically-acclaimed Portal game and multiple other shooters and death match expansions.

Individually, the titles would cost $235 ( £158 ), with Left 4 Dead alone contributing a large part of the sum.