Greater Necromancy- Just like revive dead, but instead of a zombie, it raises a much more powerful ghoul
70 mana 5 mana a turn

I'm guessing you meant novice necromancy. And in what way does it make them more powerful? Higher stats? More power in their attacks? Do remember necromancy puts you in complete control over the dead so they're not bumbling idiots, theyre capable of wielding any day weaponry. How long can the spell last at maximum or is this simply to the extent of the mage's mana pool?

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Detonate The Dead- When cast, one of your undead thralls instantly dies, sending bone splinters out in a 10ft circle around it, this thrall can no longer be raised.
Uses 20 mana. Roll 2 dices with 6 sides. Need 1, 3 or 6 to hit.Deals 25 damage.

I'll have to first off change the dice rolls. Did that for ya right here. Can the thrall that gets exploded be selected or will it be at random.

Mass summons- The same as novice necromancy, but raises 3 undead
Uses 100 mana and 10 mana per turn. Lasts up to 3 rounds. Casters attacks per round are halved as long as the spell is maintained.

Looks good.

Command Dead- Gain control of an undead that you do not already control
Uses 50 mana and 10 mana per turn. Control is given back to the undead, or if the undead was raised by a necromancer, placed back under that casters control

This spell would, to stay lore friendly, require a greater mana input than that of the caster in current control. I'm guessing it woul also allow to take control over the undead of another necromancer?

Ever-living servant- When cast, one of your currently summoned undead thralls no longer requires the mana price to be paid every round and can only be un-summoned via re-death or released from command, when released the thrall dies once again.
75 mana

Approved, though i should note that if an undead regains control it will simply be a mindless, primal creature with barely any emotions.