Eh, isn't that the fairly standard set bonus setup though?
The 2pc makes the set possible: Massive increase to DH damage while using a melee weapon, Allows Wizard to keep Slow Time up 100%, Thorns is now AoE
The 4 pc is the defensive bonus: Shadow Power gets all it's runes, Slow Times reduces your damage taken, Bombardment lowers your damage taken.
Then finally the 6pc makes the set viable, Impale deals HUGE amounts more damage, Enemies under Slow Time effect take more damage, a huge chunk of your thorns is applied on hit...
The only difference between the Necro sets and all the others is they're been a bit more relaxed with what skills the sets effect. They're much more broad bonus' which means that people have more leeway to create builds. This is a good thing.