Once you've defined the scope, the types and the number units you will be putting into the game, there's really no getting around the fact that making all of the content, be it 3D models or sprites for the UI, takes a very long time.
Much more so than the actual coding of the game. Needless to say, as an indie I don't have a team of artists at my disposal. So between myself and Ramon, we're filling up our free time (an increasingly scarce commodity!!) quite comprehensively.
Currently I'm concentrating on level objects, like the palm tree above. There's some problems with the alpha map as you can see. Depending on the lighting it's either white, or it's the fill color. Not yet sure what the reason is, but I'll muck around with the shader and the device state to try and solve it. Ramon is currently concentrating on the actual player helicopter model. We've dicussed various "modes" for the chopper, and there will be an upgrade system. Mostly though, we want a visual aspect to each of the upgrades and special abilities. This might complicate matters dramatically with the animation loops etc, but we'll get to that when we get to that :)