I like the idea, but the deck feels too scattered. Also, you have a few cards that just work against what you are trying to do.
For instance,
Lord of the Undead is a great card, but not in this deck. what is he going to return? You delve cards, your other cards want to eat your grave, not bring it back.
Also, he is slow. Worse, he pumps any Zombies your opponents control. Try the
Lord of the Accursed to give them all Menace, or
Death Baron for Deathtouch (and both of them only pump creatures you control!)
A few boardwipes would be handy, like a pair of
Damnation now while they are cheap. Which can also fuel your delve. Or
Mutilate, etc.
The
Diregraf Colossus would get you a LOT more value than some other cards you are running(like Kalitas- who is a decent sideboarder...). Endless Ranks is just bad _too damn slow, sorry- and
Necromancer's Stockpile is pretty bad as well, you could run just about anything else.
Inquisition of Kozilek is also something that should come in. and is better than
Thoughtseize in the early game. I'd probably try 3 and 2 respectively, or 4 and 2.... the extra
Thoughtseize can go in the sideboard.
Also, look at
Collective Brutality, the card is Bonkers against Burn and aggro, and fits very nicely with what you are already doing with the deck. It is especially good when you can pitch a coupld Gravecrawlers to it's escalate just to have them hit the field the next turn anyway, living the dream. lol.
Just a few considerations....