One little detail I like about Halo 5 (and even Halo 4 ) is the fact that you can actually see people removing mags and replacing them in third-person.
It bothered me a lot in Reach that in third-person characters were still “miming” reloads, particularly the Grenade Launcher animation.
I was floating around using Spectator in the beta and noticed you can even see the guns projecting light when someone uses Smart Scope (which raises odd questions about how it actually works, but that’s a different conversation).