This is the first 4E thread that I've replied to. For obvious reasons.
In my experience, in 3.xE, MMORPG's had the right idea - one big, bad pet, instead of a horde of tiny, easily-killed minions (which I suppose you could call the "Diablo 2 paradigm").
I like animating the dead, but I also like having creepy necrotic powers. Really as long as I can write the word "Necromancer" on my sheet, I'm happy.
I'd say you could get that with
* necrotic damage dealing spells
* spells that cause the weaken status on it's targets
* zones spells that cause the weaken status as well as dealing minor necrotic damage
* summon conjuration/ create undead, it has hp equal to your int score. attacks as your Int vs AC. damage is 1d6+ Int mod attacks any creature that is adjacent to it on your turn. sustain minor. move action to move it a number of squares equal to your cha modifier. standard action to have it actively attack that round (otherwise without direction, it will just continue to attack whatever is next to it on your turn).
* a higher level version of the above thing that lets you create a number of undead equal to your wis modifier
* a power that lets you make a wall of undead that attack anything that starts it's turn next to it (int vs ac, 1d6+ Int mod damage)
* a close burst power that heals all your summoned creatures in the burst area
* some variation of cause fear
* some spell that temporarily increases your AC, fluff that says it makes your body strong like bone
* ranged bone attack that shatters on the primary target and does secondary attacks from the shards on all adjacent creatures to the target
* a utility spell that pretty much acts like tenser's floating disc, but the fluff is that a skeleton is carrying it for you like a mindless butler
* a spell that does extra damage to creatures with the undead keyword (if i can make you, then i can break you)
* a spell that gives regeneration to creatures with the undead keyword
I'm just making all this up off the top of my head .... my image of a necromancer may well be different than your own.
Damage/Attack/Etc amounts would need to be adjusted depending on what level power it is ....
blah blah blah disclaimer blah blah blah I'm sleepy blah blah blah yeah i know there are typeos and rambles