I've enjoyed playing for hours, and would love to play hours more, so I wish there was a "save game" feature. It seems quite easy to play just about indefinitely, though. You might want to consider adding some sort of hazard rule to add challenge, like "in order to build a new village (that is, one non-adjacent to other housing tiles), you need a railway tile connecting them. Another hazard might be a "cursed" tile that spawns roving hazards like plagues (destroying houses), locusts (destroying fields), and fires (destroying trees). A tile would lose its curse if a temple is built adjacent. Spawned curses might be fixed by building hospitals in villages, reptile houses for the grains, ranger stations to stop fires (maybe over a longer range, given that tile placement would require open spaces).