Took me until the middle of era 4 :)
Incredibly strong concept that's been executed to perfection. The eras work so well, with keeping track of your progress through each one really adding an extra layer to consdider, where I'd have to think if I could increase the likelihood of starting a new era with particular buildings on the map or push for more resources. The range of units is fantastic, I loved the little rush of excitement when unlocking a new one, and particularly liked the options that would reward careful planning of the layout of my settlement.
Art is excellent, with buildings each immediately distinct at a glance. I love the amount of subtle movement that's constantly taking place onscreen with lighting, text and squash/stretch on buttons - it's never distracting, but gives an additional layer of visual interest that could otherwise have been absent from a game about buildings.
The music is perfect, with a bounce to it and an immediate appeal that really helped me settle into the game. I really liked the second run through of the A section - the soft piano chords that lead into it, the change to the harmonic structure beneath the guitar melody - it's just a lovely variation that keeps the piece feeling fresh.