I keep seeing lots of people all over the interwebz talk about how Andor is high-quality stuff. My question: Do I need to watch Rogue One before diving into Andor? And a follow-up question: Is Rogue One a decent movie?
I'll hang up and listen.
What makes Rogue One interesting is the move away from the simple black-and-white morality of the canonical Star Wars movies. We already knew that the Empire did bad things, but Rogue One shows us unflinchingly that the Rebels also had the capacity to do bad things in the name of the rebellion. The possibility of moral failure among the rebels is present and obvious in the key opportunities for betrayal--a situation that's about as far from the original SW canon as you can get.
And that alone makes it a refreshing change from the childlike moral vision of the original SW canon.
Andor is mostly the backstory of Rogue One's male protagonist, Cassian Andor, during the five years leading up to the events of Rogue One. There is also the backstory of Mon Mothma, the Imperial senator who became the leader of the Rebellion. We're slowly learning what her choices are costing her.
Rogue One nudges open the door to the possibility of moral compromise; Andor kicks it wide open, and that's part of why those of us who have seen Rogue One are being gobsmacked by Andor. (Think of ST-DS9 "In the Pale Moonlight" in which Captain Sisko went where no Star Trek captain had ever gone before--morally speaking, of course.)
Seeing Rogue One will tell you how Cassian Andor ends up, but I haven't seen anything yet in Andor that makes sense only if you've seen Rogue One.