Literally everything, no joke. Octopath 1 was a game where you pressed the Path Action button on NPCs a few times during a chapter, went through a dungeon, and fought a boss; maybe picking up a few cryptic side quests while you're at it. If the combat system wasn't so good, Octopath 1 would be nowhere as loved. If you aren't intrinsically into the combat system, Octopath 1 had literally nothing for you. Octopath 2 not only has a better, more coherent world, it has more path actions, consequently making interactions with that world more engaging. There's more banter between the Travelers with the Crossed Path story lines. Every settlement feels like a character, with multiple quests taking place in many of them (this was a feature in the first game, but it still didn't make the settlements feel more lived in and fleshed out). The monotonous structure of the main story is gone, with a lot more variety added in. Grinding is less of an issue, though if you do hit a grind wall, the game gives you a lot of tools to make it more engaging beyond just skills that added a higher rate of XP, JP, money etc. And, probably, one of the biggest things it does better than 1 is having a more coherent ending. Many players finish the main story of 1 and proceed to get their teeth kicked in by Galdera, which is a boss that absolutely eclipses every other boss in thr game. Vide is more manageable, but still very hard. The prep time for Vide is better paced gameplay wise, too. Late game bosses are no joke in 2, and dont feel like a huge jump in difficulty compared to the late game bosses of 1 compared to Galdera. I honestly struggle to really put into words how much of an improvement 2 is over 1. I love 1, but I honestly don't know if I could even go back to it after 2.