Gundam Seed is good if you have seen Mobile Suit Gundam and really enjoy the Universal Century timeline. They make a lot of references, nods and fanservice for the fans of the UC timeline. This is especially true with Gundam Seed Destiny, which is bad, but for different reasons. However, you can still enjoy Destiny because of it Zeta references and the fact that it is dripping with MS Gundam references from the Zakus to one of the more famous lines "This is no Zaku!" actually making it into Destiny.

But I like Destiny for a couple reasons and hate it for one reason. Shinn Asuka is the reason I hate it and also the reason I like to watch it. I can deal with an angry ticked off at the world for screwing me over character, for a while. But he needs to change and become a likeable character, Shinn never becomes one. The first I watched the show half way through I was cheering on Kira and Athrun to kick his butt in his spoiled brat Gundam. I cheered when Shinn kept realizing that he failed to kill the Seed characters and that they were totally putting him in his place. And seeing him totally lost at the end after he had one last chance to redeem himself, made me so happy specially since Athrun totally showed him up while not in Seed mode while Shinn was all berserker in Seed mode.

The reason I watch Destiny is to see Shinn get his butt kicked because he's a terrible protagonist. He makes for a decent villain, but he always just taking orders and never thinks for himself so he makes for a really bad villain most of the time since he doesn't have a mind of his own. The thing that makes Destiny interesting is the fact that the main character is pretty much the villain of the show, since the actual "Villain" is pretty easily dealt with in the end. He made for a better villain, but he was just a leader. It is the ones in the mobile suits that are actually the villains and Shinn was pretty much it along with Rey. But Rey wasn't so good, he was more devious and certainly had better villain material, but he's a terrible pilot.

In the end Kira and Athrun tell Shinn he's a bad main character and steal the show from him and take control of everything. And so everyone that you've following and supposed to be "rooting for" end up being the villains at the end of the show. So if for nothing else mixing up roles like that makes Destiny interest. It is just a shame it was not designed that way, everything I've read says that it got changed because of Kira's popularity and Shinn totally failing as a likable main character. Shinn never managed to actually grow and by the end he was just all emo and emo anger.