This is a Band-Aid on a wound that never healed right. Most of it is the same ending you already watched, dressed up with a few extra scenes and an epilogue that whispers answers to questions the show should have screamed about three years ago. Only worth your time if you need to know what actually happens to these people, because Sunrise sure wasn't going to tell you the first time.
In Cosmic Era year 74, the long civil war between the earthbound Naturals and the space-dwelling Coordinators nears its end. Kira Yamato, flying the Strike Freedom Gundam, leads the Archangel and its allies in a last-ditch effort to destroy the Requiem, a super-weapon that could wipe out most of humanity, and to stop Durandal's plans. Fighting beside him is his friend and rival Athrun Zala, who must fend off his former subordinate Shinn Asuka, pilot of the Destiny Gundam, who sees Athrun as a traitor. The battle spreads across the Requiem cannon, its relay stations and the lunar surface. This OVA reworks the final episodes of Gundam Seed Destiny with new footage, small changes and an alternate ending, then closes with a postwar epilogue.