Soulblight is one of the two themes that has Wizards with them (Vampires) and one of the few that don't require Necromancers to work.
Keeping that in mind, it's units are small but with Elite combat stats (they have no infantry, as of today) and must rely on monsters and fast charges to win. This can be compensated a bit with summoning.
Having 2+ units of Blood Knights is... quite expensive, both in money and in points, but they are well worth it, and so, one should aim to move fast and hard against heavy targets and not become entangled with lesser enemies, since Vampires, while formidable, are not like they used to be in 8th when a single hero could kill around 7-10 models a turn easily.
It seems like the Soulblight's "battleline" are Fell Bats, with stats very much like other Battleline units, with the capacity of become enraged with their Scent of Gore ability, but are not very durable. Vargheists are expensive but they hit like... a winged vampire on steroids!
Our best General is a Vampire on Zombie Dragon, hands down. Coupled with Red Fury, and an Arcane Shield each turn, it becomes a massive threat on the table who can easily destroy blocks of infantry (will let you know his average damage per combat phase soon

). Cursed Book or Tomb Blade on this guy for extra power!
All in all, it is an expensive army, but with very powerful gimmicks like the Coven Throne's Beguile spell which can basically disable an entire unit until your next Hero Phase, and the Scrying Pool to make that critical dice hit/miss, etc.