Earth is a good substitute for terraforming mars, if you like tableau builders but find terraforming mars too long. There is still lots to keep track of here, so it can be a bit of a brain burner.
Couple of levels more difficult than Search for Planet X, but still a fantastic puzzle. The changeable species, plus a few other additions make this a very replayable game. Highly recommend if logic games are your thing.
I have been wanting to get US for sometime. When Western Campaigns came out I knew I would buy it as it is a great price and I assumed a good way to learn US. I was not wrong. What I really like is I can setup a scenario quickly and on a small coffee table and play it in a short time. I will definitely get US one day, but in the mean time when I want to scratch the grand strategic itch without setting up a massive game I will go to this.