I like this very much, and no it is not too dark.
The only thing that really bothers me though is the very bright horizontal line defining the shore -water edge, which immediately draws my eye and holds it there.
I took it into CS5 and as it is it is only two pixes wide as posted, I did a 50% brightness and also a contrast decrease in most of it and it softens the look quite a bit and gives more of a broken line look which would be more consistant with the breaks in the clouds and the suns reflection on the water through them.
The horizon is ever so slightly off -down on the right. ;-)