Here are a couple other details to look at:
The pliers. Though it's a bit grisly, notice that the men up at the cross are pulling out the last nail with a pair of pliers. Jesus' arm is exaggeratedly stretched.
The doorway. What's with the doorway over the head of the man at the back of crowd? What's the doorway in? A rock face? Mid-air? I think that was Rembrandt's way of drawing attention to that particular figure, who probably was his depiction of one of the religious leaders.
Where's the light. There are two sources of "spot light" in the painting. Both are hidden, so that someone or something is shielding the light; we just see the effect of the light.
Am I seeing things? Okay, it may just be me, but is that a badger in the lower right corner hiding behind the prickle-bush?