It is an impressive storm, but it looks a little gray-on-gray. I think that if the shutter had been open for less time, the background could have been darker without sacrificing any of the ligth from the lightning itself. It gets harder to capture the moment when the thunder cracks of course, but that is the way it is with photographing lighting...
A difficult subject to take a photo of, you have made a good job of it, it looks misty and the clouds give a nice effect to it. Have a look at my portfolio there is a lightning picture in there if you like lightning. Regards Terry