Really, the thing that makes or breaks a sandbox game is the relationship between the freedom you're given to do whatever you want and the structure provided by the game that holds it together. Some games like terraria like to focus on the latter, giving an insane amount of things for the player to do. But I think Minecraft strikes a perfect balance, you're given a limitless number of things you can do, while always being given a simplistic structure by the game which lets creativity shine. It's a game that is as great as you make it