Hi Andrew, lightning over Sydney 6/30
This is without doubt a really good photograph. You have anticipated the possibility of this storm passing over the Opera House, you have set up the camera, waited for the moment and it has proved successful for you.
I do not see a need to mess with your technique too much, but I will give you suggestion on managing your exposure in the future. Lightning is very similar to an ordinary flash on your camera in that the shutter speed does not control the exposure; it is the picture and the ISO control the exposure.
In this photograph the lightening is looking underexposed but at the same time the Opera House has some bright highlights that are detracting from the lightening.
To make the lightening look brighter you need to either open up the aperture (from f16 to f11) or increase the ISO (from 100 to 200). This action will actually increase the overall exposure for the image but what we can do now is decrease the shutter speed from 30 seconds to 15 seconds; this will have the effect of decreasing the brightness of the overall landscape (remember, adjusting the shutter speed will have no affect on the lightning).
Now assuming that you have used a really sturdy tripod, there is another technique that you can apply to this image. Assuming that you have set up the camera on a tripod a few minutes before the storm arrives, I would be inclined to make a series of bracketed shots that you can use to create HDR image of the Opera House. Once you have HD are set in the bag, you can then go about the business of making long exposures in the hope of capturing lightning photographs. Later on you can combine your best lightning photograph with HDR image in which you have been able to manage all the tones successfully.
Happy shooting, Anthony.