Although I rather like the endless buckets. It'd be much harder to get rooftop waterfalls without them :P
I don't mind starting out without coal. I've spent a night frantically walling myself away from the creeplies as I got stuck out at night too far away from my lair(s). You'd miss out on that if you could *always* find coal.
Oh, that flat world was done with a hack tool. Nevermind then. :P
World themes, huh. I'm sure there will be more work on the underground layers to come ...