So slow...
Basically what Andropinus said (5 reviews below me), and also:
Add customisable controls. Seriously, it's annoying as hell otherwise. I'm left-handed, and using WASD with my right hand is really annoying. If you don't believe me, try using IJKL as up/left/down/right, H as "repair barrier", and Y as reload, and use that with your left hand.
You might as well make the "repair barrier" action automatic. There aren't any penalties for repairing the barrier, if you just got a big rock and left it on the F key (or used a macro to keep F "pressed"), you wouldn't be any worse off.
Also, you should make the barrier repair faster, the longer it's been since anything has attacked it. So, if nothing has attacked it for 20 seconds, it should repair at AT LEAST double or triple the speed. Failing that, make the repair action work with a percentage of the barrier's max health, instead of "5 damage repaired per second", or whatever it is right now.
And the scroll wheel seems to scroll the actual page down, as well as the various menus, etc.