30 Day SF & Fantasy Challenge Day 16: The Must-Adapt SF Series

When it comes to a lot of science fiction and fantasy, there are so many books and series out there that we all know should be adapted. If you could give the green light to any series, which one would it be when it comes to the science fiction side of things?

Bonus Question: Which series do you think is impossible to bring to live-action through either film or TV?