Looking for a game...etc.

I'm looking for a game that lets you create a world then mess around in it, I guess like Lego Creator but one that preferably doesn't look like crap. I know I just get any game with an editor, but I'd prefer something simpler. Kind of a free-form sandbox type thing.

I know that was a really vague description but I don't know how to specify more.

Ask in the floated recommendations thread.