I quite like it. I would have framed it slightly to one side or the other of where you did, to give the sunset (bright mass) something to balance against (there are dark masses on the horizon in both directions, either would work). It's simple, but there are some nice echoes of line in the sky and water.
It's a bit *thin* content-wise, but you're clearly not intending this as an essay on man's inhumanity to man, it's supposed to be pretty. And it is.
Winnie, If you resize the photo to say 1024 x X and use moderate web compression... it shouldn't change. What software are you compressing with? There is no EXIF in the image, so I can't tell!
The site will compress your images if you dont.. so it is best to do that before uploading them. My images are much smaller (60k or so at 800x600) than the 245k that your image above is... so it looks like you didn't compress it?
Another option would be to use a photo sharing site. Still need to resize and compress before uploading... or they will mangle your images...
Photobucket.com ... Resize and compress first.. their algorithms are harsh
Flickr.com ... A better choice, but limited to 1024 max... easy to link photos from.