Mars looks quite hospitable in the photos, but all is not quite as it seems. Our Earth based intuitions lead us astray, and the planet is full of surprises. Though great to explore, it might not be so ideal as a second home.
Mars looks Earth like
You might think from the photos, that Mars looks like a reasonable enough place to live in. It looks pretty much like a desert landscape here on Earth, and you can imagine that if you set up lots of greenhouses, and use the resources of the desert itself to make new greenhouses, you could hope eventually to colonize the entire desert.