@Chris
Okay, I think I have fixed the problem of staring at the top of the screen.
I have added a macro function which I'll explain in a bit, as well as the ability to toggle your units creation on or off.
I do agree that the player needs more interaction, somehow.
I've seen games such as Plants vs Zombies or Revenge of the Titans, which you need to actually click on the gold, or gem refinery to collect cash.
But I'd like to think of a better way to do this, the ground vehicles are going to have more interaction as you will be able to tell them to stop; personal transport vehicle is inbound as mentioned by Sean.
Repairing buildings, and researching units all takes place at ground level, so the eye really is moving around more now of course as with any RTS once your stacked, you pretty much win.
@cosec
If I lowered the ground or raised the ground, more ground isn't really great.
I've tried it, it feels weird, and the GUI overlaps the units when it is on the bottom of the screen.
Raising the ground simply to put the GUI down there has more cons than it does pros.
All the air units are silhouetted on the sky (the background gradient will change) the camera can move up to see more sky, rather than down to see more ground.
The new build macro is as follows
1,2,3,4,5,6
Q,W,E,R,T,Y
Originally I had the units all tuck nicely into the corner and move as you created units.
Now they just get placed into their correct macro slots for visual knowledge of what buttons to press for which unit. (as seen above)
Other tower/castle defense games include a man-controlled turret or "arrows" which the player can upgrade.
But I wanted to avoid this as I couldn't think of a way to do such that wouldn't be over powered.
This worked for mouse control as it was all nice and neat, but since you can now press buttons and auto-create toggle the units I figured it was best to change it.
You can toggle a unit by right clicking on the unit icon this also displays the unit's information.
Clicking the icons still works, but it's not very efficient when you could be using all all your fingers on the available macro's, as sometimes it's nice to turn off toggle and wait for the cash to roll in.
All the buildings have drop down menu's which can be accessed by clicking on them, from there you can research which units for a fee. This default menu in game maker freezes the game, but I don't care enough about this game to try any harder to make a menu that doesn't.
@cosec- also the unit's y position is randomized in creation so they do appear over the sky this just makes the units seem less linear.