I mean, for me the coolest part by far is the mesmerizing ADS color shifting. Like, most of the time in game I don't actually "look" at the skins, but the ADS is something I get a good eyefull of since it's right there around the crosshair. For me, that puts Nebula on a tier above the competition. The only thing you see more during gameplay is custom reloads since you aren't exactly shooting while those happen.
I only hip fire, so for me I get the most fun out of inspecting and equipping pre-round. I'm glad you like the ADS, though because we try to make the ADS interesting without it being too distracting or busy.