DC has written
I'm already using Ogre3D and I'll stick to that engine. Stranded is not a sandbox game in first instance. It's a survival game. Also C4 is not free and prefer using a free open source engine.
Survivar offten means game include sandbox elements like tree-cutting, stone-cracking, house building, crafting etc. SIII in my opinion must be S2-like but with... emmm... say.. liquid physics and better landscape generation, also I waiting for cool campaign (S2 stroy was rock! Selling drugs to island people was very funny!)