The green of the sea underneath adds so much depth to the palette. The back-lighting on the undersides of the sails looks really cool too.

Truly outstanding, the colours are so spot on that everything reads amazingly well. I do agree that the colour count could be downsized, although I don't see it as making any less of your work

Beautiful work ;)

this look realy amazing

well done!

The patch of sea-green in the lower left works well to balance the desat red of the cross, nice touch!

You can easily get away with 32 colors:
https://abload.de/img/2018_marcovalekaz_nav08oqv.png

This would make pixel level polish a whole lot more easier

The image already has everything it needs to be great pixel art.

Composition and mood are on point
In this stage however it looks more like a sketch, than a final piece I'd say.

Even better than I remember it :)

Very good!

Wow! Great work! 

I love the enlighted sail and waves!

I don't feel it as a battle... only one cannon is shooting... sailors seems too relaxed... but is still great!

I accept that criticism whole heartedly. I think that this being pixelart is actually only relevante in some areas of the image. as in others I used speed tricks which I never got back to fix or clean up as you mention.
I did make this live in about... 6 to 7 hours, maybe, so there is a lot of layering, and randomly adding colors to serve my view. I'd love to bring this down to say, 32 colors. Might not be possible, but would be fun.
 

Really great composition and I'm a real fan of a lot of the detailing and the general feel of the pallet.  That being said I feel like you should flatten the image and give it some pixel level cleanup and color reduction.  I was really blown away be the image at first and I think it has a lot of potential that it almost sees through, looking closer though I can still see very clear signs of layer opacity being used, lots of floating pixels, and just generally a need for cleanup.

I want to be clear as an artist you're fantastic.  I think you've really got some serious skill and doing this in only 5 sessions.  I'm genuinely impressed.  From the perspective of pixel art I think this lacks an attention to pixel level detail and it ignores many of the defining principles and techniques of pixel art.   Does that mean it's bad, of course not, but I think you'll get some criticism here for it.
 

I see! The full version still has the redundant colours I mentioned, some of your "solid" clusters are made up of multiple nearly-identical variants of the same colour. Even an automatic reduction would work for situations like that.

actualyl it might be 128, as the image I uploaded was only the thumbnail. its fixed now! 

yeah I think the count was wrong. I did try automatically reducing the amount of colors to about 32 colors and it still held up fairly well. I should have been more restrained with the colors, but I hacked at it like a digital painting. 
the process is here:
https://www.youtube.com/watch?v=xEaavp-niLA
 

Great shapes, non-conventional line patterns and segmentation. The colour really makes it, well done!

I remember watching the making of this. Very impressive scene!
The colors are great.

This has 83 colours, not 128. However, I feel like even 83 is a bit much, this looks like it should be 40-something colours. It looks like you have a lot of colours that are used for 1-2 pixels each, some for tiny details, some for AA, even though they're essentially invisible there. In addition, you have numerous colours that are almost identical used within your larger clusters, which looks like a the consequence of accidentally using the wrong opacity on your tools or an error during saving.

The high colour count aside, I love your colour choices. It's clearly a bright, sunny day, but the colours are subdued and gentle. The sails feel translucent, the water feels bright and reflective, great job!