First of all, welcome to the forums! I'm glad that this thread proved of inspiration to you.
I have a small personal dislike for taking pics of the internet and resizing them, but no worries, that's just my personal preferance.
Yeah i know that some people don't really like this method but i just take some parts of pictures, like an interesting helmet on a guy from a game, a good looking weapon in a drawing, never the entire picture.
When I comment on the pics I'll use numbering starting from the top left and going right starting back from the left at the second row.
1) His right leg looks odd from knee-down. It should probably go straight down instead of curving inside. Otherwise it looks nice. What did you use as a base, if I may ask?
The base is a rain priest from LA Mictlan, and the legs are already like that on the original sprite 
2) His grip on the trident is odd. He's holding it like a praying mantis. Try holding a broom or something horizontally and you'll notice it too. You could also shade the trident shaft a bit. If you can fit two colors, you should use two colors. The robe could perhaps use some shading.
Shading of the robe: that's a thing i have to do on all my sprites with robes, i already try but i'm not good at it, i hope i will improve with time.
The grip of the trident and the trident's shaft: i did not see these details but i think you're absolutly right, i will work on that.
3) The shoulderpad on the right probably shouldn't be that dark. It creates the feeling that he's holding his left hand way behind his back. The heads a bit blurry too.
Will work on that
4) I like this guy. He seems to be facing backwards thought. I'd suggest mirroring him horizontally and giving him more of a facial features (hair? face?).
Personally i like the pose, i find it twisted and dynamic so i think it will stay like that.
For the face: the concept of the sprite is a guy trapped in an armor covering all of is body and also his face ( but of course you did not know 
) so no change needed.
5) the robe could use some shading here. Also the shield is a bit blurry, can't really make out any patterns. Is that supposed to be writing? If so, cool. Just make the writing darker (to make it stand out more) and take some lines away. Also the blade is tad too thick. It looks like total.. overkill. You know, it's tad more ridicilious than badass. I like the chest.
the blade: yeah, i wanted to make it big but i overdone it, will fix it
The shield: it is actually not writing, just some sort of texture but the writing idea is cool, i'll try to do it!
6) The same blade thing applies here. Also the insignia in his chest armor doesn't really stand out. I'd make it smaller but brighter. remember that it doesn't have to be a real symbol, just seem like one.
Will work on the chest but i like the blade.
7) Apparently machine of some sort. Looks pretty good.
In fact, that's a huge beast recovered with an even more huge armor but yeah it looks like a machine. But i already worked on that ( see the picture attached to this post)
8) Sword thickness is problem here too. His left arm is also a bit too dark.
Will fix that
9) Sword thickness and robe shading. Otherwise pretty cool
10) Chest insignia. The sword isn't as thick as other, but could perhaps use some trimming.
11) His chest looks odd, but can't really put my finger on why.. He also deosn't seem to have any grip on the staff. Where is his hand? I really like the robe.
did not realize his lack of a right hand, it will be fixed.
12) That red spearish thing needs shading. As does his robe. His pose is very menancing, I like it.
13) Sorry to sound so harsh, but this one needs a great deal of work. His pose is all over the place and he seems out of focus. Also if the guy is using a heavy two-handed weapon, he should wield it two-handed, otherwise it just looks silly.
I think i will change his pose to make him hold his weapon with two hands.
14) Now this is one scary guy. He could use some shading below his head. I can't really say where his chest armor ends and head begins. The grip on the sword also looks odd. Perhaps show some hilt?
Shading and a hilt, good ideas.
And he better be scary, he is the big badass leader of my nation 
15) Pretty good.
Thanks ( he is my nation's pretender)
I may sound harsh, but remember my prejudice against internet sprites. It may have affected my judgement. But I promised to critizise and that I will do.
That was not harsh at all don't worry, just some honest and constructive criticism and that's what i wanted 
I'd explain in more detail, but I'm in rush to go drinking.