As I personally have almost no background in photography, I am taking the standpoint of the common viewer.
To start off, the HDR effect really ads a great amount of quality to this image, making details and colors crisp, all while pleasing the eye. I also love the position of the sun, creating vast, beautiful shadows.
The most stunning aspect of this picture is the "flow", if you will. Your eye just gravitates towards the Donau City Church, and the way at which it is angled causes the eye to move to the left, exposing the contrasting red of the Andromeda Tower. In this fashion, the Andromeda tower becomes a pseudo-focal point and greatly enhances the image.
Furthermore, the amount of distance between the New Danube Tower and Tech Gate adds some depth to the image, highlighting the people walking through the city. This effect brings some much-needed life to this city scene.
But one thing sets this picture a bit off: the UNO building. The way it is constructed, namely the lack of a more modern look, causes the image to have less of an impact. This is not an easy thing to fix though, as if it was cropped out, there would be a fragment of the building left behind the church, causing the image to feel awkward.
Overall this is an outstanding image, with a very fresh feeling.