I have a distinct feeling that we're going to see some improved lighting in the version of the Source engine used for the next Half-Life title. To be honest, with the great animation and characters, all Valve would have to do is up the texture resolution a bit and adopt a Doom 3-like per pixel lighting engine and they really wouldn't have to make any more technical changes to the engine over the next 3 years, or however long it takes to develop HL3. Three years from now, CPUs/GPUs should be able to eat Doom 3 and Half-Life 2 alive in terms of rendering power, so I look forward to see what join Unreal Engine 3 in the near future.