There is a lot of great sci-fi art on Deviantart. This has a way of standing out.
Where you have placed hexagons plays a part. Really gives some unison to the architecture and subsequently the painting. They catch the eye like a border or frame overlaps an image yet quickly get distinguishing part of the colossal structures. The layers of light as well as details such as the birds really add scale. Same with the eye catching water plane. It may take up a small part of the picture, however, like all mirrors it creates an illusion of a greater space.