In general Lack of details on the female genitalia. Community and artists pour creativity and details all over pensis and balls but so often when the female sex is drawn as a line and the opening just a hole. Second thing is anti gravity breasts, either by just being torpedo perky or when a character being upside down them still drawn as if they where right side up.

Another thing is overly large 'cute' eyes. Often pushes characters into the realm of cartoons/mascots to me and can really detract from a realistically attractive character.

Yeah I can see that, I think most people just don't refrence pussies like they refrence penises. If one thing's apparent in the furry environment it's heavy use of artist drawings for refrence and not real life. The rocket breasts and alien eyes are probably another victim of people not first looking at how real life presents the same thing.

I myself have the opposite problem where I feel like I understand how pussies work and how they're placed but I still don't have a full grasp on sheaths or the intricate parts of the penis. You need to know how something exists to draw it well and learning from other people's drawings doesn't really do that.
I'm also still trying to find a good way to draw the eyes, I know I've ended up with that "cute eyes" problem before.

Bright and otherwise unnatural colors are a turnoff for me, especially when it's the internal flesh and genitals. Neon green vaginas just don't do it for me. Makes it seem like less of a fantasy and more of a joke.

With furry art specifically, I'm not keen on pictures where the character's face is drawn pretty flat. Some people's stuff looks more like humanoids than furries.

That and what Cragger said

When people use the ever unrealistic Anime-ish style. And I don't mean the eyes.

Anime style cheeses out a lot in details. Which is why it gets pumped out a lot.

A simple example is the mouths. Drawn on the side of ones face. And it's worse when used on furs, how the make the snout point to one side even though you're supposed to be looking straight forward.

There are a dozens but I will limit myself to a few:

1) Every Male/Shemale/Hermaphrodite has to have an incredibly oversized penis. It is like the only way people can express dominance is with her penis size. Why does one need peni over ten inches on Anthro character. A human is well endowed with everything above seven inches. Yet furries need to have 16+ cocks on six feet tall characters. Why? It makes them immediately disgusting

2) Flawless/Perfection

Every male is ripped or fetishized fat. No average person is depicted. Same with females, slender or toned, perfectly curvy and giant breasts ( as mentioned above: Gravity, what is this stuff? ). Why aren't there more realistically older characters, people who are chubby, maybe aren't the most pretty around but more of a real life depction. I want to see flaws, missing fingers, eyes. Glasses in non-sexualized manners. It feels just like the fandom takes placed at a fashion show with models and ripped guys.

3) Defying Realism

A twenty inch penis entering an average female with visibly bulging out stomacht. Bathtubs filled with cum spilling out etc. Sorry your art can be perfect and appealing but the motive makes me turn away immediately without thinking twice. Same with "Oh my character is sixty years old and looks like 22" what, ever heard of aging? It will happen and staying in shape will become difficult even if you try hard.

4) Colors

Rainbow characters, neon fur etc.

5) Cute, Everything NEEDS TO BE CUTE

Why can't one show an average depiciton of a character. Sort of as if in a anthropomorphic world an artist sketches a random passerby? No everyone needs big eyes, blushes, cute and soft facial features. They need to be happy and joyful, strike perfect poses.

6) Odd Mixtures

Human facial features but the fully body of a anthro? Bipedal on an anthro derived from digitgrade species. ugh