A slider or some selections would be great.

The mods up HP and damage, but really what you want are things like the mobs are faster, more mobs at night, multiple sea serpents in the same area (does that ever happen? Have yet to see more than 1), etc.. Plus I think on harder difficulties mobs should be able to climb very steep terrain, thus ditches or steep hills for bases can't protect them, just slow em down (and trolls+ crush through logs/stumps on the ground. Basically make the pathing easier so they are more deadly). And more 1 and 2 star as soon as you upgrade gear, etc.

Faster mobs would probably make it a lot tougher. Escaping is usually easy, faster means much harder to retreat and you get swarmed quicker, so have to be careful more often.

And on higher difficulties maybe bosses have more abilities, and move faster, strike faster.

Game is great but what I find most fun is the challenge of gathering and building while being attacked, and that is only exciting at the very start of the next biome you start to work on. Once you get the next step up of food and weapon, a shield or piece of armor, starts to get pretty routine. Be great if it was dangerous at least until you are fully upgraded.