I think it was a very good series, albeit a little slow. As for the "preachyness", if you're going to make a realistic series about Mars colonisation, climate change and corporate greed are topics that are unavoidable. Climate change is not "left wing", it's just a fact. In fact, far too many movies and TV shows tip-toe around the issue, so it's refreshing someone actually having the balls to address the issue. And the politicised science usually are the one trying to disprove man-made climate change, not the other way around.
The only thing that bugged me about the show, was the use of lights inside the helmets, which would impair their vision because of all the reflection. But it seems the norm for most Hollywood movies, so I guess it's forgivable.
But all in all a good watch, unless you're too sensitive about the reality of climate change.