EDIT EDIT: Just to point out I missed the part where you said the latest sprites were on the front page... so keep in mind this is in regards to the sprites in the package... I was in a hurry.
Fair point, my apologies for not expounding upon my my comment. In my defense I was tired and trying to get you some feedback before I hit the sack. hence why I am up now early in the morning.
Now always keep in mind my reviews and suggestions are my opinion. I am by no means (I repeat no means) an end-all authority on these subjects. I apologize if this runs a bit long but you asked for it
Alright, here we go. For the following critiques I am using the Aenet as reference.
In most of the solid areas the coloration goes from light to very dark in several stroke like striations. The orange parts are the biggest offender here. Compounded with the heavy outlines that definitely look like pencil strokes instead of computer drawn lines (or better yet realistic lines) make it look like a color pencil drawing.
While having color variation is important it needs to be done subtly. To fix it I would use a smudge or blur tool and make the variation and shading smoother and more subtle from the base color. I'll explain the shading later.
Try to always avoid using black lines, they are distracting and don't look natural with the color. Try to get any outline as a darker version of the dominant color (EG the color of the higher on the ship part). Also try to keep any outline to 1 pixel wide. Use shadows to show different sections of s a ship.
EDIT: The spade is much better on this point, but try to make its outlines a bit thinner.
The whitened sections where you tried to introduce a shine may be a bit heavy fo an industrial ship. This is more your aesthetic but most ships like that are a but more matte do to hard work in harsh conditions. Though the shine does look a bit strange over the line on the lower bluish section. A shadow causing change in elevation on a section is usually dominant over a surface shine. I would consider toning those down a bit or at least making the line more visible.
For the glow sections (the what I am assuming is the dock) and the cockpit lights, consider adding a bit of white to the center of them to make them look more like a resonating light instead of a flat color. The Flight deck does it alright but the bridge lights are the real offender here.
Several sections look a bit flat shading wise. These are the upper part of the bridge section, the bottom left most chunk of grey in the open pipe.wiring section, the grey par just above the engine and the orange part with the emblem. This segues me into shading.
For shading, there are flat parts and the ship lacks depth. I explained the flat bits but the lacking depth is because it is impossible to tell which sections of the ship are higher than others. This is accomplished by creating shadows. To do this I use a black airbrush tool. For instance if the orange section is higher than the blue section create a drop shadow starting darker and moving lighter with the black airbrush. I usually don't go more than a couple pixels with shadows as you don't want to overwhelm the ship with shadow.
The same concept applies for structural shading. For instance if the orange sections are slope toward the outside of the ship (which I assume they do) shad fairly strongly from light to dark, if it is a curve, make the shading more subtle and slow. Be careful not to make the very bottom too dark though as you want your sprite to stand out against the space background.
As for some articles, I would read the blog post that David, one of the creators made a while back. It helped me a lot.
It comes in two parts but I am only linking you to the first
http://fractalsoftworks.com/2014/05/16/let-me-draw-you-a-starsector-ship/next he lists a reference to another incredibly helpful instruction (which I used more than the blog)
http://androidarts.com/art_tut.htmhttp://androidarts.com/pixtut/pixelart.htmI would start with these links and if you need more google pixel art tutorials. Most everything else I found says the same things as the three references I gave you though.
So there you go! hopefully that gave you some direction, sorry for rambling on...
One more coding technical note. If you are trying to get your ships in balance with vanilla I would have to tell you that a frigate sized carrier is not a good idea. It is impossible to balance, hence why you don't see any in vanilla. If you want some good reasons, talk to Mesotronik, he and I had an in depth conversation on the subject when I tried the same thing.
If you want to still be able to launch the Nail fighter from the Aenet, consider changing them to a drone. That would make it more balanced. If you want to keep the PD drones as well, keep in mind that you can give drones drone systems effectively giving your ship two drone sets. Just be careful not to go overboard with that.
Anyway, keep it up! You have the talent and potential you just need to refine it (hell I still have a long way to go). Everything is a step toward getting better.