Nekros is a very good frame when it comes to his abilities -Other than being the sharpest tool in the farming shed- Crowd Control and Support are present in most, if not all of his abilities.
1)Soul Punch: Although not the best ability, it can be used if needed. It is quite proficient at blasting high-priority targets (I.e; Ancients, Heavy, Gunners, etc) away from a location, (Example: If a downed ally/objective) however, this ability is almost never used due to Terrify's larger radius.
2) Terrify: Virtually an upgrade to Soul Punch on the grand scale, Terrify serves the same purpose, but scares multiple enemies away from the desired location.
3)Desecrate: Do I even need to tell you?
Nekros+Corpses=Profit.
(Survival/Defense) Nekros+Campingspot+Corpse Pile=IMMORTALITY.
4)Shadows of The Dead: This is good depending on who you kill, if you kill mere cannon-fodder (I.e; Chargers,Lancers, and Prodman) the ability will become useless, however, if you kill hostiles such as Heavies, or anything that assists their allies, you're shadow crowd will become a major help. (I.e: In a Defense mission, a Shadow Squad of Nullifiers, Healing Ancients, and Heavy Gunners will make for an awesome defense)