The reason Doom3 is dark is that the number of polygons that needs to be calculated for the shadows goes up exponentially each time you add a dynamic light. If you pay attention during the game, you'll note that there are very few places where there are more than two lights shine on the same place, and there are large dark areas with small static lights between the more well lit areas.
I think that they overestimated what the hardware would be capable of when they were creating the content, and then had to pull a bunch of lights from the game when they saw what the current gen hardware could do.
As for which engine looks better, you'll have to wait til January to see what we say about HL2
I can't wait for Ravensoft to get their hands on the new Doom engine and do some magic with it. I've got a BFG GeForce 6800 GT OC 256mb card that needs a good workout.
Trilinear filtering and max settings...it's like a power shake for it (it's pensive and nervous at first but once it gets going it's like...ho-hum).
Throw High quality at it and it catches it one handed, in the dark, while watching T.V.
Throw 1600x1200...it files it's nails while doing the above.
Hit it over the head with 4x AA - it looks at me like it's annoyed (bring it fatboy, it says).
8x AA and it starts to exert itself. But hardly breaks a sweat., spits out 41fps in timedemo1 the first time through. It gets tired and heads to the dugout, not bother with the second run. Kinda like A Rod.
Then I install the 61.77 drivers. It gulps it back, not really needing it but knows it'll make his trainer happy.
And I run out of config options. The game gets called due to rain.