First off you don't have to upscale when posting here, just put em up with 100% zoom because the forums have a built in zoom function. Secondly, you seem to use a lot of dithering when it's not really necessary (although not in all your stuff).
There's more, but not sure what more general things to pick out here, maybe more contrast (and sometimes there's too much?) in your colours, if you want to have a more specific critique, put up only one thing and describe the situation and its use.
If you want to make something more detailed just make it larger and give it a few goes, post it on here and we'll help you proceed from there.