Did various bits of tinkering yesterday - varying pitch of weapons fire (depending on shot size) and enhancing explosions for Bomber and Destroyer.
The main chunk of work has been the secondary weapon (a traditional charge up blast weapon). There's a twist in that the shots break up and scatter on impacting a smaller unit.
I've uploaded a new video:
The gameplay difficulty still needs tweaking. It is very tough on Hard difficulty (as shown in the video) although I can battle my way through without losing a ship most times.
Need to finalise the name of the game shortly - can't keep calling it 'Vertical Shooter' forever...