Wow! What memories. That video features the very same version of Dropzone I used to play back in the 80s on my Atari computer - it's definitely one of the best games from the 8-bit era.
The gameplay in Dropzone was based on the classic game Defender, in which you must rescue scientists stranded on the surface of a planet - in this case Jupiter's moon IO. Featuring horizontal side-scrolling, the game was first released on the Atari 800Xl before being converted to the C64. Although similar to Defender, this was a lot faster and more polished.
I remember that the game was quite difficult, but addictive to play - with plenty of practice you would find yourself getting some pretty decent high scores. Reviews of the game were mostly very positive in the Atari magazines and Zzap! 64 magazine (for the Commodore 64) rated it 95%.
The designer of the game, Archer MacLean, signed up with U.S. Gold to distribute the game across Europe. However, after 18 months the royalties dried up and U.S. Gold claimed that the game had stopped selling, even though it continued to sell for at least another five years. A big legal battle ensued and MacClean eventually won an an out of court settlement after around four years of battling. Apparently, MacClean bought a Ferrari with the proceeds!
Dropzone title screen
Dropzone screenshot of the C64 version