[protonfish]

That's a good question and probably critical to answer before discussion. I wonder if an open-ended world could be best described as one where the player finds enjoyment playing without an explicit win condition and/or can solve problems using many different strategies. (Preferably not "canned" solutions but ones where clever use of skills and the environment could even surprise the developers.)

[DaFranker]

Those seem like two somewhat distinct regions of definitionspace. But yes, they sound about right for what I usually mean by "open-ended". X-Com would be mostly an example of the latter, while a sandboxy game like Minecraft would primarily identify with the former.

But at this point I think it's more convenient to ditch "open-ended" and find other words to associate less confusingly with those notions. "sandboxy", above, is my first candidate. I have no good ideas for the other kind at the moment.