Ok, there you go: The Pillars in the front are not perfectly straight. The background looks nice, soft and painterly which is a massive contrast to the flowers in the front, that look more like oversharpened photographies. The distribution of the sharpness throughout the picture it, what makes it a little off. Fro example, the tower on the left side, behind the pillar looks quite soft again, allthough it's the same distance or maybe even closer to the viewer in as the pavillion in the middle of the see, which is in contrary quite sharp. What I probably want to say is: What is the main vocal point of the image? Is it the flowers? Then everything behind them blures out gradualy. Or is it the pavillion? Then everything farther in front or behind it would gradually blur out. They compete for attention.
Edit: I probably should clarify the flower part. I know they are not oversharpened. It's the light, they where shot in, that makes them look so contrasty. Decreasing the shadows and highlights might do the trick there.