An Update
I am working away on this. Sadly, I cannot really share much of what I'm doing with you guys, for fear of spoilers. Even the most innocent comment from me would reveal things about the game I don't really want public. There has to be an element of surprise and exploration in the game for it to have the maximum amount of fun. So I have to be careful about what I say.
So I can't show you levels or talk about the side activities right now. But I will soon be able to show you a model or two I have been working on. I'm not done with them yet, but hopefully it won't take me too much longer to have the first one ready. I'll show it to you guys after the modelling is done, but before I UV map or rig it, so it'll be in a T-pose and very monochromatic 
I have a list of all the set pieces I need for at least the first level that are mission related (although come to think of it, I suppose I need to make some decisions on what side activities will be there and get a list done for those as well). So I'm going to be starting the level design fairly soon. I'll start by grey-boxing it (which is a fairly easy process). So it shouldn't be too much longer before we have an actual level to run around in. Good stuff.
"They laughed when I said I was going to be a comedian ... They're not laughing now." - Bob Monkhouse