I actually just rewatched Destiny recently haha. other than the soundtrack (which is absolutely incontestably superb) I think that it is possibly the most wasted potential of any Gundam show. It knows everything it wants to do and all the points it wants to hit, it just can't seem to ever find it's feet and execute it competently.
I think the opening premise is really, really strong. Orb's destruction in SEED was a big plot point but showing the real personal impact of that event on Shinn was a great idea. Sometimes in Gundam the combat and the action and the cool impacts and stuff make you forget the people who have their lives utterly destroyed by the "good" actions of our protagonists. And that further tied into the entire premise of Orb doing everything in their power to stop that ever occurring again, defying their principles and their honour and everything we as the audience say is "right".
But instead of showing the strong-headed, assertive, tomboyish Cagalli work within that framework and national trauma caused by her father's principles, they decide to utterly decimate her character and hand her the biggest idiot ball I have ever seen. Like seriously even if we ignore all the stupidity that came before it, the whole jumping into the battlefield and trying to talk Orb into stopping is seriously the stupidest thing I can imagine. AND THE SHOW KNOWS THIS! Athrun's exasperated cries for them to go back to Orb are echoed by the audience but the show refuses to make up an answer as to why they wont. And the problem is that it isn't an isolated incident, again and again the show sets up an interesting moral/emotional conundrum and then absolutely flubs it's way through it.
I am emotionally invested in the characters they built in SEED, the show is great at setting the mood with great music and lighting, and the main plot points are pretty well thought out (Stolen suits, Junius 7 colony drop, War restarts, Orb loses neutrality, etc.) but the actual storytelling is so bad most of the time that you can't help but get annoyed.
One thing to finish off is that I really like how SEED/Destiny treats the mental/emotional health of their characters. To often TV treats war and the actions in it as barely consequential other than death/injury. But with SEED you see Kira crying, getting mixed up with Flay, sleeping in his machine - all things done to specifically clue us into the impact that the battles are having on his mental health. In Destiny we have Shinn who mentally scarred by his experiences, and something I only caught in the rewatch is that I am pretty sure that Kira is depressed at the start of Destiny. People often take his reluctance to kill people as a super arrogance, but I think what they wanted was to show that the mental impact of killing people is so great on Kira that he simply can't do it. He locks the Freedom away and gives the keys to Lacus and has to practically beg her to let him fight again. Often fighting, being the hero and coming home alive is shown to be the absolute best but I think showing a character reluctant to fight and angry that it's all they are good at was well done with both Athrun and Kira.