Put into development for Half Life 2, the Source engine has become one of the most widely played engines on the planet. It powers not only HL2, but its expansions - Episode One and the upcoming Episode Two - as well as extensions including Counter-Strike and Day of Defeat. It's also widely used by third parties - Dark Messiah is built on the engine.
Writing the Source engine took Valve a long time - a long time. The release of HL2 was put back a year to allow for things to be finished. However, the firm's switch to episodic content - delivered through its online distribution platform, Steam - has allowed it to add to the engine pretty quickly and regularly since the release. HDR and cinematic effects are two of the upgrades that we've seen to the engine, both of which are designed to make things look better and richer. This dedication to the 'richness' of the gameplay experience is an ethos that permeates Valve - programmers are regularly found enthusing about how what they're coding will add depth and interactivity to the game. As Gabe Newell insisted today:
"Fundamentally, games are about what you do, not what you see. So in terms of things which make games fundamentally profound experiences - and differentiate them from non-interactive entertainment such as TV and film - it's more about what you do on the CPU than on the GPU."
Valve's multi-core transition is about allowing hardware enthusiasts to get hold of software that really takes advantage of the awesome new power we're going to see over the coming months. But more than that, it's about driving games further and deeper, making them - simply - better.