There's so much more u can do with this simple style.
main thing is we need more depth here.
u have 2 layers which r nicely separated but then suddenly there's nothing but sky.
for example u could have that midground layer make more hills instead of just a few props poking off the foreground layer.
behind that u can have another layer with a spooky church or one of those big grave tomb things with a crow sitting on it...whatever.
the bottom of the scene is crying for whisps of mist IMO.
don't understand the lines between the stars but yeah viewing on my phone the AA dark green pixels has made some chunky clusters u want to smooth out.
moon is rendered oddly as if its a ball that is floating inside the atmosphere instead of something way off in space.
if it doesn't interfere with ur theme, it would be interesting to have some clouds up the top which get lit by the moon.
I'm not a fan of the mixed dithering in the sky gradient but I like the simple dithering of the glow around the moon.
This technique can be used to make wavy lines to break up the sky gradient to give a nice impression of clouds.
I don't have any great examples handy but if u look at top right corner of this image it gives u a bit of an idea of a very simple application (don't read into it too much it was just a quick edit of someone's thing from ages ago)...
