For the paintings its ok but how about the windows? you really have to make a hole in the wall, so that makes 5 out of 1 brush... And one of them is darker I dont know why...
Tr to make it by hand anyway, the only other things i can think of is the lighting quality setting, your video card.
THe funny thing is when i created levels for this other game Vampire and this would happen that meant that the -extra should be turned on for compiling.
When i searched around for compiling options it does something differend with the sunlight.
I get the same thing quite often, I presumed it was cos I was doing a fast compile and that it would go away on the final compile. I hope so, I'm worried now
Like JV_map says, making the brushes detail often helps. But, there are times nothing helps, so the best thing you can do is make the cuts vertical instead of horizontal, and make a few extra cuts. Take advantage of the uneven lighting and give surfaces a more used look. Vertical boards often fade or discolor at different rates.
With key S you can change "intensity" and "density" of the lightmap on a brush face. I am no expert at it, but the shadows do become more defined with intensity 1. So, maybe intensity -1 will reduce the shadow. I have no clue about the default value of density.
You could also try the "nolightmap" checkbox for one of the faces.
Tltrude has another good point. Sometimes I'll copy a texture, use Photoshop to give it light/shadow effects and remove the light map from the shader. It often results in better effects than letting the engine light it.
I believe the default lightmap resolution is 32, the lower you go the better the quality but the longer the compile time and the bigger the bsp file thus requireing more to load in the memory.
But that could indeed be a factor as well.