'Terraforming Mars' is a game that I've come back to more times than I can count.

The beauty is that it visually looks really complex and advanced, but the gameplay isn't really that much complex more than wingspan.

Over the years I bought the 'prelude' expansion which speeds up the beginning. (Highly recommend)

And then once you've played it more than 10-15 times, the Hellas& Elysium adds more maps for variety.