So I have been looking to add an achievement system into my C# files.

I was wondering, other than building "Achievement Points" up as you go through them, what else would you want from the system itself?

for example
> Specific items you can only buy/craft when you have a certain amount of AP (cosmetics)

I also was wondering what kind of achievements would interest people? as mainly, Mir ones would be kill x amount of mobs.
>also what do people think of "hidden achievements?" - do they just annoy you?



EDIT:
I am trying to scope out what I should and shouldn't look to add into the system before the implementation process starts ^.^