Rognoll's Sketchbook

[Samszym]

I think the way the image worked changed because in the first one the foreground character has the highest value contrast out of anything in the picture, which gives it a bit of atmospheric perspective. He has an easier read than anyone and a lot of areas where he pops out. In the second image the knight character has more contrast and no character really stands out as light against dark anywhere, so it's harder to see what's going on at first glance.
A good test for this is to squint your eyes or maybe apply a 25 pixel gaussian blur to the image and see if you can still identify the figures and shapes for what they are. If you've composed your image with good clarity you'll still be able to make out the important figured, even with everything blurred. Howard Pyle once said "After the first half-hour of work, your lay-in should kill at a hundred yards", meaning your value structure should be so clear that even if someone were looking at a print of your image from across a long hallway he'd still be able to tell what's going on.

I'd recommend doing what my teachers call a notan, basically drawing a thumbnail sized version of your image using only pure black and white, no grey or hatching at all. Doing this forces you to decide what is light and what is dark and helps you make a clear read.