I am not sure if you have your monitor set up too bright/contrasty, but most of the pictures are indeed too dark - not that it would be nonrealistic, or hard to see, just a little too dark and dull so the first thing I and most people think is "go to photoshop and use levels".
In my opinion it contributes to the realistic feeling of the images - they look just like a real, nonperfect camera would make them. Not sure if that is the intention or not ;)