My cousins always want to play Civ III, and after several ~10hr games, I still don't really know what I am doing.
It's a game of decision-making. Each decision leads you on another branch of the tree. To make it more unpredictable, your decision-tree is mutated by each other player's decision-tree.
Like any traversal-oriented game (RPG, etc.), it just takes a lot to understand the effects of your choices, and what goals to make.
After a few games you kind of get the hang of the initial phase, and some techs are always decent to aim for at first, but the really tricky part is quickly assessing your starting conditions and adapting your goals from that.
It's a game of decision-making. Each decision leads you on another branch of the tree. To make it more unpredictable, your decision-tree is mutated by each other player's decision-tree.
Like any traversal-oriented game (RPG, etc.), it just takes a lot to understand the effects of your choices, and what goals to make.