Im having a lot of trouble getting the lighting to a good standard in my map, take this shot for example:

As you can see the ceiling is extremely bright, the floor dark (it is water though) and the walls having lines where it goes from light to dark, in other areas of my map, models show up extremely dark aswell.
What am I doing wrong?
Is it just a matter of getting the radius and intensity right?
Some lights on the tutorial use an info_null, is this required?
And what does lightmapping do exactly? (as in shift+L, S then Natural)

It can be, but also we all tend to use custom vision files or menu vision files, which really improve the overall quality. Try that maybe and mess with your world spawn settings

This be wrong section, I disappointed 

lol, just noticed. moved

This may help you http://wiki.modsrepository.com/index.php?title=Call_of_Duty_5:_Advanced_Lighting

The ceiling is like that because you used a "wet" texture. I had the same issue at one point and found that was the cause.

Also if you haven't already, Remember to use a lightgrid.