I've been doing more waves for the demo level and I'm now halfway, although it suddenly occured to me last night that I do still have code to do. I've not done the weapon energy bar yet! If you've watched the video you'll notice your shields take up both bars, but the plan is now that the one on the right will be your weapon power and it'll slowly drain over time. This means you HAVE to go in and collect coins to buy more power. IF you manage to get a load of coins before say the final 1/4 has gone, then you get a power up.
It'll be interesting to hear what you all think of this mechanic when you play it, as we both feel its whats going to make the game fun/difficult/annoying. Most games you can stand back and blast away, but with this one you have to get in there to pick up coins which means you will always be in danger!