Their explanations made sense regarding Earth, but if you are looking for an in-depth theory on what life on other planets would be like with an in-depth explanation based on their various properties, you will be disappointed.
They lightly touch each property, such as heat, oxygen, and gravity, but the environments are not extreme like you would go in expecting to see. It feels like an alternate reality that could exist on Earth if genetics played out in a much weirder way.
As for that, while a handful of their evolutionary hypotheses were plausible, the mutations of the actual creatures they modeled did not make complete sense. In other words, the predatory animals became conveniently "dumb," and the mutations, which often attempt to minimize energy consumption in animals, became unnecessarily complex and "unrealistic" for okay visual gratification. As much as you can say for a fantasy series, that is. Watch episode 3, "Eden," for a very obvious example. I'm not a scientist by any means, but it is relatively easy to understand if you have some concept of evolutionary reasoning and purpose when you sit and think.
As for the CGI, as others have mentioned here, it is practically non-existent. As the episodes went on, it only diminished further, to the point the last episode was pretty much just another cliche Ancient Alien space exploration episode.
The series started decently then quickly slipped into another background noise program. The guests were great, and the explanations good on a very basic level as expressed, but the "realism" and attempts with modeling and environments fell way short of what the advertisements lead to believe, almost to the point of feeling like their passion disappeared halfway through. I have watched these kinds of and nature documentaries passionately for many years, so this was my experience and afterthoughts with it. I hope there is a turnaround. This show has a lot of great potentials.