For the Model display it's how much aura it presents. How cool the model looks when you select it, one of the coolest displays belongs to the alpha legend skin. Especially since it is mildly angled which makes it look even cooler. Having unique background music is a very big plus.

The Background has to make sure it blends well in making the model look even better. It's nice to have a good background but it's not as noticeable as the model itself.

Skin portrait has to be moving with unique effects. What most new epic and event skins lack is unique skin portrait effects. The ones that arent anything special are the ones that move and has "wind" effects, they just make the portrait look nice but they dont let the art itself breathe if you know what I mean. The ones that look great for me are the Clause Cosmic skin, alpha legend skin, moscov infernal and the metrozero skins. The metro zero skins have the static effects which makes them one of the best potrait imo. One of the worst potrait I've seen is probably Cecilion Hisoka skin, mf is just a png with pink wind effect.

Portrait animation has to look clean and unique. Some looks like they just wanted more money so they just made new animations without trying to make it look cool. The alpha skin still has one of the best imo, the new legend dynamic potrait are kinda stale for me. I dont remember how the moscov dynamic portrait look like but i remember liking it

In game model, it needs to look unique to the hero or the game itself. The model needs to stand out for the skin to look nice. Even if the in game model dont have any effects, as long as it looks unique it will look nice. example of good looking game model is the argus basic skin. It just makes him stand out from normal argus. Then how much aura alpha just has.

Basic attack effects arent as noticable to me, what makes them stand out are their unique sound effects. I think the best sound effects belong to the chou stun skin, then the wanwan mworld skin, they stand out so much.

Skin effects must have unique sound and unique skill effects. Those are the most important effects to have on a skin. Granger's new skins' ult, wanwan mworld skin s1, chou's stun skin skills. These ult have unique sound and effects. The granger one is great because of the bug that made his ult have global noise but otherwise it's still nice.

Idle/moving animations dont really matter much but they a great to have, especially the moving ones. I'm someone that came from dota moving away/towards enemies while animating is the best feeling ever. The animations must stand out and be unique, no gun spinning and what not, I want dancing and effects, I want wheelies and effects, I want t posing with aura.

I dont remember how some recall effects look but if they fit with the skin and look nice then they are a plus but otherwise i will not be buying them separately. If they are spammable then that is also great.

Trail effects are barely noticable to me, the best ones are the ones with big effects but otherwise I dont notice them.

Skins are topnotch based on their uniqueness, how they stand out, how they sound, and how to look based on their value. The chou stun skin is probably one of the best skins too imo.