In the posts above there was talk about "tasks" that give rewards. Like adding more quests. This can be implemented right, and this can be implemented very wrong. Note that "quests" are a game mechanic that is borrowed from a different genre of games, the RPG (Role Playing Game) which became MMORPG (=massively multiplayer online roleplaying game). Of which World of Warcraft is the best known.
Civ is at its heart a strategy game. Sid Meier, who created the civ series, said that a game is a series of interesting decisions (of course he was talking about strategy games specifically, it is not true for any and all games).
Strategy games are about making cost/benefit decisions. You handle problems, which are often caused by scarcity. The biggest question in the economic part of civ is: what do I invest my hammers in? Every choice has benefits and drawbacks, and you sacrifice one thing to gain something else. In a good strategy game, the "best" choice should not be obvious, and ideally, the various options should be equally competitive.
I have played several MMORPGs in the past and they all tend to become easier and easier over time and degenerate into a theme park "click for reward" system that is addictive (look up "skinner box" (*) for more on this subject). Your "progress" equals the amount of time you put in, with barely any challenge. The fun comes from the steady stream of rewards for the time invested in clicking, with barely any hard decisions.
(*) skinner box:
https://en.wikipedia.org/wiki/Operant_conditioning_chamber
The worst way this task system can become is it becoming a kind of Christmas tree with 25 presents below it, and the game consists of picking the best 8 presents.
A good strategy game is also a sandbox game. You decide what to do next. Being given a list of "tasks" that you should do because the rewards are so strong, is not really a strategy game.
Of course, C2C does have some choose-your-reward systems, like picking a leader with certain traits. But these are pre-game decisions that set the initial stage for the game, not the objective in the game itself.
To summarize, a strategy game becomes better by adding more hard choices, with options in which you sacrifice something in exchange for something else, and it becomes less of a strategy game when it is about grabbing a steady stream of easy rewards.