Ugh, where to begin.
Contains spoilers (if you can spoil trash)
The story is a weak copy of Gundam SEED (which was a pretty decent reworking of Gundam Wing's story). Been there, done that. Throw in a 'twist' invovlving amnesia, and you've got the recipe for every soap opera out there. Maybe this is just bias on my part, but Mechs do NOT belong in soap operas.
I'd say a good 10-15% (if not more) of the series is flashbacks taken directly from Gundam SEED. Combine that with a dorky put-the-pieces-togather style mech that recycles footage every time it's deployed. Add in the standard complaint of recycled battle footage the Gundam name is notorious for. When you add those up, you've got 5-8 min of recycled footage per 20-25 min episode. If you can tolerate that, add 2-3 points, because the animation is decent. Nothing special, but decent.
There are 3 characters they try to develop, Athrun (returning) Shinn (new), and Meer (new). Athrun goes through pretty much exactly the same development he went through in SEED, making me wonder why they bothered (either of the other 2 surviving ZAFT piolots would have made the series more interesting while filling a similar role). Shinji, I mean Shinn, merely goes from angsty and unlikeable with creepy little sister issues, to angsty and unlikeable with sociopathic issues. Personally I find it hard to relate with an unlikeable character thats one small step away from turning into a full blown serial killer. Meer just plain goes crazy. While it would have been good if they had developed that more, in most cases it felt like they were trying to cram her in. The fire escape scene was well done, and some of her early stuff wasn't bad. The rest... wasn't. There are plenty of other returning characters, that should have been further developed, but sadly Lacus, Kira, Cagalli, and Murrue merely got recycled footage for thier 'development', and they chose focus on a weak 'forbidden' romance instead. Oh, and the amniesia romance. That was just plain unbelieveable.
SEED wasn't bad, it may even have been good (I'm definately biased against it considering it a Wing rip-off though). SEED Destiny... well, I consider it a waste of money, and my copy was sold long ago on ebay.