The basic idea is to increase the game difficult over time. This is my idea of how it could be: The concept: The game will start easy and you will gain experience over time, lets say you win experience for day survived. At some point you will level up, but you will not get stronger, instead of that, the game unlocks new dangers, improve the existing one or maybe unlock new other things. So, the game gets harder when you spend more and more days. The objective: The objective is to give a real value to the question "How long can you survive?". With the game getting harder and harder, survive will become a challenge at some point and finally you will die, giving yourself a personal score to beat the next game: your level. Will you do better in the next game reaching higher level? Getting harder? What do you mean? Some examples of things can be unlocked by leveling up: -Hounds introduced to the game. -More treants will appear. -Animals are now faster. -Bushes need more time to restore berries. -Fire hounds are now more common -Your will get hungry faster They are examples to ilustrate the concept, maybe not every one is a good idea Unlocking other things not directly related to difficult: Also this can be a way to unlock new recipes to research, making more recipes available as you level up,the recipes can unlock every level or at certain level, and it can be unlocked one by one or by groups. Characters can be unlocked this way too, only the first time you get to the required level, of course. If Willow get unlocked, for example, at level 5, you will unlock her during the first game you get to level 5 and she will remain unlocked forever. This way, people will get motivated to play again and again and try to get to a higher level. New characters and new recipes? who can resist to play again and try to get further! But maybe this system is too hard for some people or dont fit with the way they : Like everyone don't want to rush to get stronger before the game gets to hard, the experience can be granted for a lot of actions: building, killing enemies, researching, gathering... So the level up speed will adapt to the style of everyone. You are an experienced player and you can get everything in a few days? You will level up faster and the game will become hard early. You love to take your time to do things, explore, and play in a more relaxed way? You will level up slowly, so the game will not become very hard early, but at some point, the game will challenge you too! Difficult can be added in a easy way too: Sandbox: Experience doesn't exist. You have a menu to unlock everything you want but it will be limited to the higher level reached in a not sandbox game. Easy: halves the experience you get. Normal: you get experience at a normal rate. Hard: you get 50% extra experience. Final thoughts: I think some system like this one will increase a lot the replayability of the game. Ok , maybe not this specific system with the experience bar, but something like that. Thanks for reading and sorry if my English is not very good.