I know this is a little off topic but one minor pet peeve of mine, that I have seen a lot of lately, is when a rune's artwork has an unexplained element in frame. Often it comes about when one piece of art is used for several different runes and the extraneous elements can't be cropped out of a single rune's artwork. I will post a few pictures soon to show what I am talking about.
Here are some examples of artwork with extraneous elements that look like cropping couldn't be done in a perfect fashion. For comparison, often the artwork looks great when the champion is attacking something, and it can be seen fully, as in the following examples... /endrant
Back on topic, I thought it was cool when a champion's in game sprite would change when equipped with the appropriate equip. For example, Ash would look different when equipped with Murder. I know it couldn't be done with every rune but it was cool.
The cropping thing doesn't bother me. There's also the fact that I generally enjoy when art gives the suggestion of a bigger world beyond what is included there (when done right).
Unit death sound is really great. As for the cropping discussion, it really annoys me. Wish they were rectangular at least.
The animation of AoC is to much, also Hydraxor dancing with 3 heads. Would I be wrong if I said I miss the bases on champs back in the day?
Necrosis proc for D'at mist. Vertical push sound/animation Evil laugh from when soul collection grabs that nora globe - also think it's used for sacrifice at altar.
Maxxarek's just having to snap his fingers to deal massive damage Vertical push and Grintmaw Hymn preventing damage sounds Equipping Thunder on Mangleshell gives him a huge golden gun
Don't know if this counts, but I really love the Umbral Wulf sprite. It has a really nice design and I love that its bottom half has a 'phased' appearance.