Solid idea. Props for not making it a match 3, as well :) I'd prefer it, tho, if the resource gathering was just a little less mechanical and a little more cerebral. Plus, I didn't find it very challenging, I could do with a much harder difficulty level.
Slickly programmed, and quite compelling, which I find rather surprising considering it's a shoot'em up which considers the act of actually shooting anything to be completely incidental.