The achievements right now feel pretty easy, I remember when I first got the game I got all of them in 50 hours, and the new ones don't take much longer. I'm thinking of some achievements, some may take some work, some not.
First off, a few achievements that require you to get a specific number of followers
For example, one for 7, one for 13, one for 20 and one for 30. Or something like that. It gives a good feeling of progression, while its not really grindy, except the 30 one.
Second, an achievement for beating Extra Hard difficulty. Perhaps with it, there should be some form of feature that allows you to lock the difficulty of a save, and you could choose to lock a difficulty. Or you could do it in the middle of game but it would disable that achievement. (Similar to how minecraft has it, you can freely change the difficulty but you can also lock it)
Along with that, an achievement for beating Perma death would be great, since its just hardcore with a cooler name.
Perhaps an achievement for beating the Pentilene (Or whatever is the dont starve gamemode called)
More "masochistic" achievements:
"Finish every row in purgatory"
This one may be too extreme, but that shouldn't stop much people. If not that, maybe a finish 3, or 5 rows.
And one for beating Perma death on locked Extra hard difficulty
#A few achievement ideas.
weak raptor