Ahh, the only mistake you are making here is being discouraged by some person's opinion (not saying you shouldn't take what was said seriously, but that is not my role to judge). This is a great opportunity to improve and see to it that something like this won't happen again. After all, if you don't take this chance to brush up this piece, isn't it likely that something like this happens again? We wouldn't want that now.
Now the thing I find that a majority of clients love most is clean, high contrast and 'crisp' looking art, so when in doubt, contrast slider all the way right and gamma all the way left (not literally, be reasonable
I use to put specular highlights on everything, even fur and stuff). Shift a few hues so you won't have to hurt someone with the contrast while making it readable. The pose of the animal given to you doesn't give much character to work with, but often a super cool dynamic pose/silhouette with depth and some "built-in layers" as I call it (like some old fighting game sprites where there are limbs that are just shades entirely darker than their counterparts).
More notes after edit:
This is a lesson I learned from league, always tilt. Tilt the perspective a tiny bit, if it isn't the whole thing, at least some limbs or extremities. Even if the client requests you don't do it at all, do it slightly anyway. It makes things more interesting to look at. Just make sure the perspective isn't too off and no weird exorcist shit goes on.
Another one. Two tones, inspired by famous man in his industry of work, two tone malone. It is, as I have found pixeling over the years, extremely difficult to make something good looking with one ramp (or one ramp and <= half of another). You did quite an impressive job stretching out your palette. Free yourself with another color! Let it improve your clarity, make it easier to compose and make it easier to pose! Having a secondary trim color is so important!
That is about it. Sorry about the WIP gif, got into the 'zone' so there is a bit of a jump from the last 3 frames to the ones before, had to control z to the earliest stack to the the 3rd to last image
Also the perspective of the head fin and several other things are slightly off.
Good luck!
