Doom 3 vs. Source: Comparing Engines
Tom V. writes "DevMaster.net has an article that outlines some of the technical differences between Half-life 2's Source and Doom 3 engines from various game development aspects such as graphics, A.I., physics, networking, etc. According to the author, the winner is the Source engine based on its 'completeness' as a game development package. However, in terms of graphics, the clear winner is Doom 3."
The thing that gets me is that Counter-Strike wasn't developed by Valve.
Those who want to see how well Doom 3 can pull off Half-Life 2 style environments should check out the Doom 3 Can Do It Too project. I don't think they have a site but their forum is on http://doom3world.org. Anyway, if you just want to see results here's their latest video: http://www.pcgamemods.com/9875/ (still a work in progress, obviously)
John Carmack admitted that the Doom 3 was so dark because the game couldn't handle light on the engine level. There is, apparently, some pixel bleed-through and seaming of textures when light-entities are placed more generously. He said, on his blog I think, that he essentially made a game to suit the engine, but that the engine would develop with each new game release
Unfortunately, I do not have a link on-hand.