The aim of the game is simple, build a city. You do this by purchasing residential areas, factories, government buildings, public services etc. and from there you just have to watch things grow. This is a long running series that started life in 1989 and has sort of grown into one of those franchises that everyone with even a passing interest in games knows about.
Anyway the one big problem I have with the phone game is that it takes a long time to do anything. For example, you level up by building residential areas and upgrading them, which in turn increases population. Increasing your level will of course, unlock new features, which isn't a bad thing since it's sort of nice to have all the games concepts trickled to you rather than just having a big info dump and then saying "OKAY GO!". The problem is, you need money to do anything and you get money by upgrading residences so you can't help but start levelling up and just when you start to think everything is fine BAM! it hits you with fire stations or sewage and you don't have nearly enough money to deal with these problems.
So the only course of action is to halt all expansion and just sit and wait for taxes to roll in which of course is taking a hit because of the lack of the new thing it just introduced that you can't afford. The pain of this goes away a little as you unlock things like a trade depot and cargo missions but it still takes a while to get anything done. That said though, having a building on fire or every member of your town shitting their pants due to no sewage system doesn't fuck you completely. Your happiness will take a hit but with a little bit of patience you can fix the problem and be on your merry way.
Not bad for a phone game and great to just fiddle with between short tasks. I'm actually surprised by how fun I'm finding it and the production quality on it is top notch. Of course you can pay if you want but it's possible to get a fairly decent looking city without spending a penny and after that it's just patience. It's free so it's not like you have anything to lose, go try!