The last entry made the most of colorful choices. This one is more subdued, leaning toward a monchromatic field. The shift is subconscious. Maybe I was feeling more cautious. Maybe the subject matter just felt less colorful. Possibly I was concentrating more on values than color choices.
A word, too. on shapes. Those decisions, however, were very deliberative. If you trace your finger around the two darkest buildings, you'll see that both the shape of the sky and the shape of the buildings are very irregular, i.e. not circular, triangular or retangular. They interlock with each other in jig saw fashion, forming much more entertaining shapes. In order to make that happen, I had to make up the building on the right. I added the silhouette of a building on the left for the same reason.
I've said it before: Don't be afraid to add elements that aren't there for the sake of design or interest.