You can pick up objects, carry them around and drop them with my pick up and drop script. There is also a pressure pad script which you can stand on to open a door, step off it will close. Using it with the pick up script allows you to drop an item on the pad, then keeping the door open to allow you through. It certainly adds some basic puzzle elements not possible by default or without scripting it yourself.
Rolfy's stuff probably uses limb detection, which I have been asking for for roughly 2 years. Well I think it does, that is how I would do it, if not it's a clever workaround
I have played around with using the player angle to allow you to select an item myself with reasonable, but not perfect results (with items rather than limbs of course). I wanted it for my animated filing cabinet, so you could select each draw to open. I'm not even sure it is actually available in the current release yet, but if so the store then I may have missed it?
I would say with some creative scripting you could certainly make an adventure in GG. I really only want to do that sort of thing myself. A combination of action and adventure, most games today are far too action biased imo. We need a nice break between fights at least
SPECS: Q6600 CPU. Nvidia 660GTX. 8 Gig Memory. Win 7.