Iki Island improves on a lot of the content that the base game had which is exactly what you want from a DLC, that's why I think this DLC is even better than the base game. It has longer and more interesting side quests, a really interesting main story about Jin's father and his actions against the raiders of Iki Island. Jin tries to redeem the name of his clan and retake the island from the mongols. There are some new activities which are fun and not overused, the island is even prettier than Tsushima. 100% is a breeze and a joy, the combat is also more difficult which was really needed imo.

You will not be disappointed by this DLC so go ahead and play it. ;)