I just want a game that lets me invent something instead of following a tree.
In a sane way, not "Oh, mod it!"
I had any idea a few years back for something where one would harvest various
very basic materials shapes (rods, sheets, cylinders, balls, etc) from the environment (sticks, skins, stumps, clumps, whatever) and operating upon them both additively (sticks and sheets in one way to form, e.g. a tent) and subtractively (cylindrical tree-stump cut into discs) and combined to near-infinite and non-proscribed degree (several different ways to make carts out of wheels stuck onto rod-axles and many different bodies).
Trouble is, it'd still need a lot of thought (thinking now of a similar level to the Scribblenauts team's attention to dictionary terms) to make sure 'everything makes something', (although most of them would be inert clumps) i.e. such a huge tree that it
should cater for all expectations (again, think Scribblenauts, where "Zombie Jesus" would be possible, albeit likely to surprise).
And, besides, with the likes of Minecraft (as well as loads of other "craft things from things" interfaces in other games), the crafting system would now look like a rip-off.
(I still have the world-generator somewhere, though. Vector-based instead of voxel-based, on spheroid worlds, but it'd still look like an MC-ripoff.)