This style grows out of the tradition of classical orchestral music and features synthesized orchestration. It often features melodies and harmonies that are neo-romantic in style.
The best orchestral electronica uses electronics as an important element in a wider palette of instruments, to create new types of orchestration that would be impossible using traditional instruments. It takes the ideas of traditional orchestration and expands them, using the new capabilities that electronic instruments and studio treatments offer.
Some of the composers that work in this style are Vangelis, Mike Oldfield, and Mychael Danna. Vangelis is the most prominent composer using this approach. His soundtracks to Blade Runner and 1492: Conquest of Paradise are good examples of the style. On both of these soundtracks, Vangelis uses traditional orchestral instruments and voices, but he dramatically expands the orchestral range through the use of synthesizers and electronic processing.