For some time I have been experimenting with long exposures. I have discovered getting a good result is harder than it looks. All sorts of problems occur: camera shake if your tripod isn’t solid enough, colour casts from the reduction filter, lens issues if you stop the lens down past its optimal performance point, and lots of others, including uninteresting images.
Long exposures seem to be very unforgiving, getting the exposure right is important. This often means you are chasing the light as it fades. If you need to increase a 120-second exposure by one stop, it has to become a 240 second exposure; 4 minutes. In that time the light can fade more than one stop late in the afternoon. But I am learning, I think.