All your characters suffer from the same symptoms. Let's look at your predator-type dude there.
Your art at this size over-relies to outlines, doesn't use lighting to separate the different parts of the anatomy of the character, and is quite pillow shaded. There is a disregard to how pixel clusters work together that is indicative of sloppy work or uninformed work.
Most of all your art needs disambiguation. I need to look at your robot dude and be able to tell what everything is, what is leg, what is arm, what is just armor plating and what is tech gismo. You need to simplify and you need to use the palette so the bits of the character that have priority pop out. Instead of thinking 'I WILL OUTLINE THESE PANTS' you should be thinking of each pant leg as a volume that takes priority over the things that are behind it. You don't need dark outlines to convey volumes, in fact if anything they hurt the volumes, you need a proper understanding of how simple geometrics are shaded under different light conditions, and then you need to wrestle with making your pixels convey this.
The problem is that you work at such a res where pixel concerns are very tightly intertwined with real life art skills you lack about how volumes work and lights work and anatomy and such. You're hiding one behind the other. A single pixel here is very powerful, and what you mostly do with them is band and hug your lineart. Take the predator dude for example, and draw a pencil sketch of him, as accurate and detailed as you can, sorta like reverse concept art. Do that and then we can look at where you're failing to convey him in pixels. If however, your pencil sketch predator suffers from the same problems as your pixel art does (bad volumes, anatomy, priority confusion, posture) then it might be time to accept that there are fundamental studies you should be doing, not so much wrestling with pixels, at this stage.
