You can feel the huge jump in polish, quality of life features and moment-to-moment gameplay feel from AC2/AC3 to this. Even though it uses basically the same engine and it has a lot of the same gameplay features, it feels way better and the open world is even ahead of its time (later AC games basically took this formula and run with it). The story is also way better than anything previous in the franchise. My two complaints would be the ship combat, which still felt like cumbersome sometimes, and the way the ending just goes and goes and goes and also features some of the most frustrating combat encounters in the whole game.