Cookie Clicker is (or was, ignoring recent updates) pretty simple.
Not that it wasn't fun to play, and not that I haven't logged well over a month of playtime on the game. Not even that it wasn't, or shouldn't have been, popular. Because it was all of those things.
When you get down to it, though, the game was extraordinarily simple - almost a distilled version (or, put one way, a parody) of modern casual gaming. Click button, number goes up. Click another button, numbers go up on their own. There's something very visceral about making progress on your own until you're able to bootstrap yourself into more progress. If I didn't know that Orteil wasn't intending it to be satirical, I would start going on about how it's an insightful commentary on both the nature of casual gaming and how you can make things more successful by paring them down to their core features.
CivClicker (the original) was more complex than Cookie Clicker, and deliberately so. One of my goals was to get some design space between the two games, and I also assumed that I could make the game more engaging by deepening the mechanics. For CivClicker 2, I'm hoping to continue that trend - capturing the core experience of an incremental game but further deepening the game and making it more complex (hopefully without making it commensurately more complicated!).
At it's root, though, the incremental games genre is about numbers going up. Press button, receive bacon. Wait, receive more bacon. There's an aspect of the Skinner Box hidden deep at the core of this genre (or, at least, the best of them), and what makes these games a satisfying experience is how their progression curve is presented, from shallow to deep as the user's understanding and mastery expands. This is a pure expression of game balance as viewed through the lens of the psychological phenomenon of flow.
There's another factor to flow that I think is often missed. Assuming that difficulty must increase with player skill is all well and good (and certainly holds true for the highest-intensity gaming) but casual gaming does not demand an intensive playstyle from its players, even if they are objectively skilled. From this viewpoint, intensity of play must be factored alongside player skill to get an appropriate difficulty rating. A game designed around low-intensity play does not need as sharp a difficulty curve as one designed around high-intensity play - put another way, a game's complexity (which is a proxy for its difficulty) can be lower if the game is designed to support and encourage a more casual playstyle.
In the end, as much as I'm hoping that incorporating a map is going to make CivClicker 2 a better, deeper, and more engaging game (and the learning curve may end up being marginally steeper (or longer) to account for the additional depth), the core hedonic experience should still be one of obvious improvement and progression, with rewards for both interacting with the game and letting the game run itself. Ideally I want to find an appropriate balance of complexity to support the incremental playstyle and a longer-term progression curve.