Some ideas for you devs :
as for the enemy variety ,they could do assassins type elite that just rush you down for melee kill or hold you down similar to the choke guys from uncharted survival mode.
they basically just rush torwards you and hold you down for 30 seconds, if no one helps you, you die.
they could change it to , enemy just holds you down and slowy deals damage, you can mash to get out or get helped by an ally.
Another type they could make is an enemy engineer that heals it's ally when its done with the objective, the healing could be like Kuzman's ,shooting a laser that heals his allies.
Another new enemy type is something that bewitch you OR turns invisible (you can still shoot it ) , the visual queue should be a wavy stealth effect similar to predator with a very distinct sound playing it.