Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Left 4 Dead 2
Encore Mutation: Follow The Liter
Added support custom campaign particles. Custom campaigns can specify their own particles_manifest.txt file as well as any per map files. The per map files need to reside in the maps directory and be in the form: <mapname>_particles.txt
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Changes:
- Added support for raw mouse input
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Updates to Team Fortress 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Source Engine Changes (CS:S, DoD:S, TF2, HL2:DM)
Added check to prevent multiplayer servers from transmitting 1 as their maxplayers value to connecting clients
Fixed clients being able to use particle exploits on sv_pure servers

Team Fortress 2
Added The Shogun Pack items
Fixed the "Best Little Slaughterhouse in Texas" Engineer achievement no... [read more]

This patch includes some crash fixes, menu changes and more. Read the readme for details.
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Updates to Team Fortress 2, Counter-Strike: Source, Day of Defeat: Source and Half-Life 2: Deathmatch have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Source Engine Changes (CS:S, DoD:S, TF2, HL2:DM)
Fixed a problem with the DirectX8 cloud shader
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Jason Rohrer, John Romero, and Jenova Chen compete to make a game religion.
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Red Orchestra 2: Heroes of Stalingrad (PC)If you hate thinking, this is not your game.
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Doom (PC)Why John Romero and Tom Hall's first look back at id's game-changer was such a letdown.
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Crysis 2 (PC)Crytek gives a few answers.
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Updates to Half-Life 2, Portal, Half-Life: Episode One and Half-Life: Episode Two have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Half-Life 2, Portal, Half-Life: Episode One and Half-Life: Episode Two
Better support for Intel Sandy Bridge based machines
Fixed a bug where some video configuration could get reset by restarting the engine
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