They're all a little underexposed, also, they all look a little too warm. Did you shoot auto white balance?
Grey clouds and fog... If I expose it a little bit more, sky will be burned. Although it might be my screen! I'll check that out next week too, as I get back home...
The sky is a small part of the photo though, you want all the main content correctly exposed. There's no way you can expose everything correctly, so just focus on the main content. 90% of those shots are road/leaves/tress, so I'd brighten them up.
Also, I'm guessing you shoot RAW, right?
Awesome, man. Even if your colours/exposure are slightly off you can just fix them in Camera RAW/Lightroom.