Here's why I'm hopeful for this series.
Andor is a character that we only know a little about. We saw his final mission, but we really know nothing about the man, who he was, and what life experiences made him that man that we saw in Rogue One.
This series will be able to explore all of this and build his character. This is why I'm so hopeful and why the previews fill me with this such hope.
Compare that to The Mandalorian. He was a character that we'd never seen before, knew nothing about, and learned who he was along the way, while he himself learned who he was along the way. As our knowledge of him grew, his character grew, shedding off some of the long-held beliefs of his clan, while at the same time, trying to be true in spirit to them. It was a win all around for us, the audience.
Compare that to The Book of Boba Fett. There was an established character, and while what we'd seen up to this point in the movies left us not really knowing that much about him, we saw him as a man of few words, precise actions, always being a step ahead of his competitors. This gave us the head-canon of Fett being "The most feared bounty hunter in the galaxy." Then we got the series and saw Fett as old and soft, a mediator rather than a man of action. And... we weren't satisfied at all with what we got.
And then there was Kenobi. Again, another established character that we first saw as a mentor, a teacher, and a man who made the ultimate sacrifice so that the next generation could escape and thrive. We then got the prequels, while not the most awesome of movies, (in my opinion, Kenobi was the best part of them.) We saw a padawan grow into a master and then a member of the council. He was a teacher himself who now struggled with a padawan that he saw falling and didn't know how to help until it became all too apparent that he wasn't going to save him. And though he had inner struggles as a result, he was determined to move forward and fulfill his new duties as best he could.
And then we got a series that saw him as an old soldier with PTSD, who was now unsure of himself, going through the motions of life and afraid to even think about again being the man he once was. He had to be forced into action and then, we got a story that broke the canon of what we'd already seen! (argue all you want that this still fits into what we know about the canon, I personally don't care.) On the other hand, I LOVED little Leia, she was a bright spot in the series, but honestly, it NEVER should have been about her.
So as much as The Mandalorian worked, compared to how Fett and Kenobi didn't, I think that Andor will surprise us and work as well. We are basically getting a new character, inasmuch as we're going to learn who he was, and how it made him who we met in Rogue One.
Man, I really hope I don't eat these words later...