I haven't written anything on this thread before but I have been thinking a bit about your game and your questions.
First I think you should think about, if you make a city builder game or a strategy/simulation game or both. I will explain, what I mean;
In a city builder you focus is on building beautiful, interesting (but of cause also functional) settlements. If that's your primary goal, I think you will need a modding community to be successful. I can't tell you what the game need to attract such a community, I'm not a modder or that kind of player.
I'm rather the strategy/simulation person. I like difficulties in the gameplay, I like problems, I like disasters, I like to test the limits. In Banished: How many people can a small map support? what is without, schools? without trade? without farming?how can I rebuild after a major city fire or mass starvation?.............. If it looks nice; good! But for me, that's not the main thing.
So, how can you attract players like me? And maybe a citybuilder as well? Because it looks like you have the ambition to attract us all.
Have your game something new? I mean really new, that no other game has, not only a nicer graphic and animation.
I think it should be possible to choose among different difficulty levels. You can't really do this in Banished. The difference between the harder and easier options are small. Since I don't know your game, it's hard to say how this could be done.
Banished tries a bit with climate, types of maps, small "disasters" on/off. This could of cause be made with a bigger impact in your game.
Other possibilities could be differences in production efficiency, population growth (more children=more mouths to feed), maybe different levels of tax, that had to be payed to some absent king or some regulations of what kind of production/how many of each kind could be establish on certain places. Smaller (or bigger??) obstacles put in your way.