I had some additional thoughts.
First, while I played, I never felt the need for the Orbital Strike. I went back and gave it a try. It is far too small and weak to be worth using. Maybe after you add upgrades and the max energy goes up it will be better, but only being able to use it once, wait a bit, then get a second shot, limits it. The blast radius is small enough that under normal situations I was only getting 2, or maybe 3. On the later levels there may be larger clusters, but never really felt threaten enough to try it the first time. I had really expected something bigger, so maybe I was just setting my expectations too high.
As before, I did not use Walls. Towards the end I did start thinking about it, but just added an extra Tower at each spot and that worked. If difficulty continues to progress, I may start using them next time.
I think the change to having the Droids only auto-fire without being able to manually shoot works well. The long range firing really allowed the Droids to be overpowered before. The current range does feel a bit short, but still usable. I generally only had 1 Droid active at a time, but occasionally would use one as a guard when I put down a second of a different type.
I like the addition of the goals at the top guiding the player for what to do in the mission, and opening things up for additional goals later.