Nice effort.
I'm just a beginner at these nightscape panoramas too, and also use Microsoft ICE to stictch photos together (got to say, for a free program, it really does do a good job).
One thing that may help here is to increase your exposures to around 20-30 seconds - this will bring more light into the scene and also make the compositing process easier for the ICE software. Ideally, a faster lens will also achieve this result.
One thing I've noticed with using the ICE program (it's probably the same with other stitching software) is that the manipulation/reshaping of the images that's required means there's often quite a lot of cropping required to finish up with square sides. So I'm learning to cater for that when taking the original images. But it looks like you've achieved that with your pano.
