First of all, sorry I didn't have a chance to answer until now
I'm will quote once for the sake of shortening the message.

...

Thanks for the detailed critic and tips!
It was really helpful! I understand what you said about the form and colors and I will definitly apply that in the future.
And yes, it was for practice(I more the coding guy than the artist.. But I love pixel art so I'm trying from tome to time to do stuff).

...

Thank you for your reply.
TBH I don't like to mess with the sprite because *usually* it turns out even worse xD But that might be only me lol
But I understand what you said.

...

Thanks for the reply.
I love your edit and I can clearly see the difference in the form, shape and shades.

Again thank you all for your time, you really helped me 

Hey 

I tried to do some kind of mech thingy:



I'm yet again not really confident about the shading as I suck at shading things
I think the overall shape is fine.

Hmm that's it for now, I know there isn't much to say because it's a small sprite but I'd like to hear your opinions and critics.

Edit:
So I searched for a cylinder like metal plate shadings and I came up with these:
And

I used Starbound's space train for reference as you can see the top of the train is cylinder like.

Maybe three colors is a bit limiting. I'd say you need a very bright color (or pure white) for speculars, which could be common to all materials.
Is this shading drawn from life, or do you 'guess' it? In the many color versions it does look pillowshaded which is usuallly the result of guessing: concentric rings of colors. Stuff doesn't look like that IRL: look at the photo I posted above: the color zones are not rings, some transitions are smooth and some are hard.

Hmm It's not a guess but I might overdid it... Unlike the picture you posted which obviously hasn't been taken in a normal room, in my room the light source isn't that bright and there are other furnitures. Because of the helmet strong reflection I can't seem to find a good angle so it won't reflect the furnitures and that messes up the lighting.
Do you see the problem?
But yes, I might overdid the very bright spot it suppose to be more concentrated.

The angle of view is much better now.

I think so too, thanks for telling me to change it 

You'll have to check the linework which is very jaggy (especially the crest, both the top and the holder).

By crest you mean the thing on the forhead or the thing which holds the hair?

More than that, you have to think hard about outlines. Do you want/need them?
At this level of detail, they use up precious space for small detail shading, and they create a banding festival.
I don't like obviously colored outlines either, they have no point at all, except maybe to tone down some inside outlines, when done well.
Outlines are an abstraction, they don't exist in things. If you go for them, make them plain, dark, and outside only/mostly.

Hmm I always used outlines.. I think I can remove them though.. I see what you mean by "they don't exist in things", next time I won't use them in the first place

Depends on what you plan for this piece afterwards: keep it a single sprite on transparency, give it a simple background, or create a scene around it.

To be honest, it doesn't have a real purpose.. So I think I'll just keep it a single sprite in the end. But I do want to keep playing with it a bit more before I move on the different things.

Thanks a bunch for your comment!

Edit:
I tried to be as exact as I can with the light reflection in my room and it turned out like this:


The plain areas are actually this plain.. And it looks a bit empty.. I hope you understand what I mean..
And as I said the light is very bright but also very thin..
I also tried to get rid of the inner outlines.

Thanks for the reply
I concentrated the light a bit and added a few more colors: