Aesthetically the models will all be based in the same theme which will be an overgrown city. A mix of vegetation and crumbling buildings. On top of this they will mostly be camouflaged, although I'm not sure what pattern yet. Hopefully this will give a very cohesive feel to them.
Now all of these musings are not based on any experience, it's just what I have gleaned from the rules etc. I could be completely wrong about how they play but that's part of the fun. If nothing else they all look really cool and I can't wait to get painting them.