There are ways to have interesting and cool looking animations without being too flashy guys, some of the suggestions here are a good example. Poison, Blood, swirly starts on sapped targets...
Also our cooldowns can and should be flashy. Here are some crazy ideas.
Adrenaline rush should increase our size just a tiny bit, or have a faint yellow glow aura for the duration.
Vendetta is all about that 1 target so maybe it should make every other enemy's opacity drop a tiny bit. Right now you can't even tell who you used Vendetta on most of the time.
You know how ethereal's leave a trail when they move? I always thought Shadow Step and Killing Spree should leave a shadow of yourself that only lasts like 0.3 seconds, each time you teleport. Kinda like mages have that blinky light when they blink.
Burst of speed and sprint do look outdated when compared to speed of light, but I think the new running animations will do most of the work for this skill