>>718794703
The second game. First one is average at best but the endings of that game are needed in order for you to start connecting the dots that are drip fed to you in the second game, and when you do start connecting them it feels incredible.
In the gameplay department, the non-linear exploration and atmosphere of the map. And the locations are quite varied and have lots of varied secrets.

I think the massively improved map and it's non-linear layout is the biggest positive for the second game.