Based on the forums it seems that the current biggest issue in the game is that raiders turn it into a cheap tower defence game, and in turn many people have been thinking up wild ideas of ways raiders can be 'improved' to make it more challenging and negate the current choke point tower defence game play that lets you actually survive them.
My solution to the 'raider problem' is to make them less common, less powerful, and not out for blood. Make raiders just that, raiders. They get in, smash and grab, but pull back at a reasonable resistance. Taking resources, possibly kidnapping a settler or two if they're not resisted firmly and quickly enough. If they don't become lemmings running to their death in a hail of gun fire, then 'tower defence' naturally becomes far less of a needed element to survive.
(To make them really interesting and effective we would need a more detailed resource and item modelling system, rather than having just weapons include things like tools, clothes, etc, and rather than having 'magic numbers' for food, metal, etc, they exist as measured units in storage lockers/bins that can be spread over the base. But that is over and above this topic.)
So, if raiders aren't the biggest threat, and are more of a 'set back' mechanic, then what can cause a game to end? Improved character stats and greater focus on basic survival.
Add some form of a heat model, need for water, various kinds of nutrients, etc. Characters can be in one of several states of weakness/strength. Let them dip too far into weakness because you're not fulfilling enough of their needs, and you can quickly find yourself in a hole you can't get out of.
Push the game in the direction where finding water, more than one kind of food source, protection from the elements, sanitation, medical care, etc, will be the prime motivators in building a 'good colony', and then 'build a maze of turrets to kill baddies' is no longer needed.
Include more options for a character's mental state than simply going berserk. Let them become depressed, less motivated and productive which can set them in a feedback loop where they do less, become more depressed, and possibly drag your other survivors down with them.
My solution to the 'raider problem' is to make them less common, less powerful, and not out for blood. Make raiders just that, raiders. They get in, smash and grab, but pull back at a reasonable resistance. Taking resources, possibly kidnapping a settler or two if they're not resisted firmly and quickly enough. If they don't become lemmings running to their death in a hail of gun fire, then 'tower defence' naturally becomes far less of a needed element to survive.
(To make them really interesting and effective we would need a more detailed resource and item modelling system, rather than having just weapons include things like tools, clothes, etc, and rather than having 'magic numbers' for food, metal, etc, they exist as measured units in storage lockers/bins that can be spread over the base. But that is over and above this topic.)
So, if raiders aren't the biggest threat, and are more of a 'set back' mechanic, then what can cause a game to end? Improved character stats and greater focus on basic survival.
Add some form of a heat model, need for water, various kinds of nutrients, etc. Characters can be in one of several states of weakness/strength. Let them dip too far into weakness because you're not fulfilling enough of their needs, and you can quickly find yourself in a hole you can't get out of.
Push the game in the direction where finding water, more than one kind of food source, protection from the elements, sanitation, medical care, etc, will be the prime motivators in building a 'good colony', and then 'build a maze of turrets to kill baddies' is no longer needed.
Include more options for a character's mental state than simply going berserk. Let them become depressed, less motivated and productive which can set them in a feedback loop where they do less, become more depressed, and possibly drag your other survivors down with them.