I like the composition; I like the curve around the frame, from the rocks, along the shore, past the castle, and on to the distant lights. I get a real sense of scale and my eye goes on a journey.
I'm not really sure what the long exposure has brought to the party, though; The water has just gone a flat dull grey, and there's not much movement in the sky.
Personally speaking, I find that my long exposure photographs don't work well when I don't have a clear idea of what I'm trying to achieve by using a long exposure.