Merc: The first thing I would do is change the 1st person gameplay of the Merc to 3rd person, the Merc can take cover on objects and has a pistol and either a rifle or shotgun. The Merc also recieves two grenades and two flashbangs. The Merc also can choose between a drone or a tactical turret that can be placed on the ground, wall or ceiling.
Spy: Spies are still very acrobatic and can have their many hiding spots, now they can carry either a pistol or a submachine gun. Otherwise the Spy is pretty good, the only part taht felt unbalanced me was the no gun part.
Mark and Execute: Both Spies and Mercs can use Mark and Execute either after one melee kill or three normal kills.
Game Modes: Team Deathmatch (kill the other team), Capture The File (DA's game mode), and Panther (one spy vs a team of mercs).
Personalization: PEC points are earned for every kill in multiplayer as well as file hacks, no one outfit is the same, greater customization is added so everyone has their own agent.