I think you had the right idea. You have a bit of the nature in the foreground, the city lights behind that and then the sunset clouds as background. Did you use CTE white balance? The only critique I would give is that maybe the tree on the left side is taking up too much of the frame and kind of throwing the photo a little off balance? Or maybe the horizon isn't in the middle and straight?
ISO and exposure time are quite all right, though. Just keep in mind that when taking photos of a sunset, the light is quickly changing, so the metering of a long exposure will be wrong. The camera assumes the light won't change during the exposure, so you have to make the exposure time a little longer. Good stuff, makes me want to get a 21mm