gau-17 has an interesting feature (bug?). in defense mode, start firing with mouse pressed, then pull the gun out of the firing zone, then pull back again...no spin-up needed for subsequent shots.
makes defense mode easier.
okay so bosses are back but for crying out loudly, they are extremely hard. I had 12 3-star missile towers (well placed ones) and they only hardly killed 1 out of the 6 bosses...with all 25 lives left I was hoping for 100% completion, but then I was like hey wtf...