I was thinking the younger kids will find it too complex while the older kids might find it too kiddie. Don't know. Now I'm thinking it's really good. You can go crazy building and modifying all manner of vehicles. It's a matter of finding parts and letting your imagination take over. It's pretty lenient on how to hook pieces together, so there's not a lot of frustration involved. But there is a modest learning curve. I'd say a couple of hours minimum.
The demo has no time limits. I just spent about 4 hours in it. It also lets you save what you create, though I'm not sure yet if I can load them again into the demo. They were saved to HDD, though, since it asked me where to save (and that's what I chose). Each of the challenges lets you choose which vehicle to use. Between tries, you can refine the vehicle. For example I added an egg shooter and ammo to a pusher--a car shaped like a Y to push big things. I also added an extra engine and gas tank for more power and speed. I had to get soccer balls into the goal past these round bots that get in my way and push the balls away. So instead of just pushing them out of the way, I was able to shoot them.
I created a boat, which kept sinking and I didn't know why. Then I read the parts list more carefully. The buoyancy rings can be inflated or deflated at will, so you can stay afloat or sink at will, by pressing 'A'. Neat. I imagine more advanced parts or designs will allow me to breathe underwater, but as is, it's a submarine where you have to hold your breath. I was able to explore an area underwater I didn't even know was there. Similarly, when I found a parts box with wings in it, I was able to make a plane and explore stuff way high.
Physics are very forgiving, but still make some sense. I'm going to have to play the demo yet again, and see how else I can combine the parts. It's also nice that what you save are blueprints, not vehicles with the parts already in place. That way, you don't need duplicate parts. (For instance, all cars can share the same 4 wheels.) Good stuff, decent control. Just takes some up-front learning.