The first one could do with a bit of contrast work – it’s dark overall but a bit of contrast will liven it up without taking the sombre feeling from it. The second to me is the pick of the crop. The DOF is perfect and the detail in the foreground teeth of the cog are just perfectly exposed although I may be inclined to loose the bright spots just to the left. The third would also benefit from a little contrast and a little brightening in the foreground in my opinion to bring out the detail. I’d selectively lighten as you’re close to blowing the distant detail. And for the last one…that’s just mad!:D