The main strength of the Necrodeck is its manyfold card advantage.
Of the core cards 15 are able to achieve card advantage directly:
The Hymns (sorcery), The Specters (creature), The Disks (artifact) and
of course the Necropotence (enchantment).
Nearly all the other cards can do it indirectly like Ivory Tower vs. burn
(although the burn tends to go for the critters), Protection from White
creatures vs.
StP, toughness 4 or greater creatures vs.
Bolts, Strip
Mine by denying the neccessary mana ressources to cast spells in the
first place, consultation by replacing itself with a advantagous card,
drain life by fueling Necropotence and destroying life/critter.
The only disadvantagous cards are the Dark Rituals which allow for speed
(and can become advantagous in a drain life) and, if you want, the
lands and the Zuran Orb.
Note also that many of the optional and Sideboard cards exploit this
card advantage principle even further: Serreated Arrows vs. Weenies etc.
The combination between direct random hand destruction and disks/prot.
white creatures works even more devastating then each alone. As you
combat the Necrodeck, your hand will probably empty while you try to
defend yourself or to mount an offense and through the hymn. When the
disk finally hits the table and destroys the rest of your ressources.
To hope for the luck of the draw to deliver the neccessary
disenchant/
detonate/whatever is a pitiful endeavour indeed.
The same can be said for Hypnotic/StP or Sengir/second Bolt.
The second strength of the Necrodeck is that it is monocoloured with
overall cheap casting cost spells. This, together with the consultations,
means there is little chance for manascrew. It also means that the
multiple cards drawn by necropotence can to be cast right away, thus
allowing the necroplayer to draw another slew of cards.
Some people have deemed the Necrodeck to be vulnerable to direct damage.
This is a misperception. A dd player has to kill the creatures or he will
die faster than he can blast his opponent into oblivion. But if he does
so, at some point both hands will be quite empty. Then a Necropotence
drops, followed by another horde of creatures, that will kill him.
The Necrodeck, as different as it may look, has been said to be the
type two equivalent of "The Deck". Like this infamous type 1 deck, the
necrodeck is not concerned to protect it's life total, as long as a
single life point remains. Instead, it takes a fair amount of punishment
to establish total card advantage, depleting the opponents hand to zero
and destroying all permanents (save land), while filling the own hand
up to 7. It then proceeds to kill the hapless opponent at leisure.