I selected editor, but that would be only part of what I would like to see. I'd also like the AI to be very good with railroads in particular, but make them harder to build (whether separate, more expensive unit, longer turns to build them, or whatever.) For this to work, the AI has to be good enough to build a rail net, instead of around the cities. Then the incentive ought to be changed. Instead of +1 mine or +1 irrigation on individual squares, it ought to be increased trade in cities that are connected.
Combined, that would make the rail net a strategic, commerical asset, with no reason to flood every square. You'd still have movement issues when fighting off of the rail net.