Let's see.. Facial tattoos, custom paint your weapons (like making your gun look N7), ranking system is a lot more fun, jetpacks, climbing buildings, ect... And Mass Effect needs more game types than just hoard mode.
You can change your entire face colour in ME3, not just part of it. 
There are guns in ME3MP that already say N7 on... so no effort needed to make them look N7-y.
Jetpacks? TGI, Havoc. No biggie. (LOL at COD for jetpacks though. Think that's hilarious).
Hoard mode is fine by me. As long as it isn't PvP, I don't especially care. But PvP game modes would a) attract twelve year olds screaming down their mic, and
ruin the Mass Effect experience.
You have me on climbing buildings, but you could always take the stairs. Y'know, and make it easier. Maybe take an elevator up a few floors. Mass Effect 1 had great elevators. 