Terrapin:
In deity plus three, you can expect all of your citizens to be default black hats. While two luxuries will make a black hat happy (not just content), to use happiness buildings to counteract unhappiness they must compensate all the levels of unhappiness "outstanding." If you have a large empire, as I did, the riot factor will make your citizens unhappy several times over, until a cathedral will not even turn one black hat blue. JS Bach, on the other hand, can make two citizens content if you station a unit outside the city because of a bug in the game that turns black hats red for unhappiness due to units outside cities. Bach then makes those red hats blue.
Offbalance:
Deity plus three is a modification that can only be made to classic. Essentially, you go into the rules and edit the menu to give extra levels of difficulty. In classic, you can also edit barbarian levels in order to give barbarian hordes of 99 units. I don't play against humans.