"Close your eyes. Your eyes can deceive you. We must not trust them."
When this series was announced I wasn't sure what to make of it. While the idea of how the Sith were able to survive the last big Jedi/Sith war and remain undetected is an interesting one, the novelization of "The Phantom Menace" already gives some insight of how the Sith pulled it off, and the novelization of "Revenge of The Sith" show Yoda's realization of the Sith's master plan, much to his own dismay.
But after watching this trailer, I have to say I like what I see and it's going to be interesting to see how the Jedi in this time period deal with this. While I never read the High Republic books and I am only now getting into the KOTOR video games, I know that Legends continuity talks about what is now known as the Battle of Ruusan, which was said to be the last big battle between the Jedi and Sith, which led to the eradication of the Sith. Or so the Jedi thought.
While I don't know if the show will utilize the previous source material, the trailer does give a good presentation of what is to come in this series, and for the Jedi who had been at peace for close to a thousand years to be caught off guard, it is going to be interesting to see them a bit out of their depth as they try to solve this new mystery and find the enemy that's going after them, not realizing that this is only the beginning.
So in all, I'm optimistic about it. here's hoping it's good.