Darkness Eternal is a complete Vampirism Overhaul for The Elder Scrolls V : Skyrim. It aims to make Vampire-gameplay more interesting and in-depth. The Vampirism-system found in vanilla Skyrim is completely over-written when Darkness Eternal is installed.

The key features of Darkness Eternal include :

• Pre-Vampire Gameplay.
  Darkness Eternal includes a Pre-Vampire gameplay mode known as Infected Mode. In order to become a Vampire, the Player must first obtain the Blood Infection. This unique and incurable disease spreads through the Player’s body as time passes, and its progression can be combated through the use of Potions and Shrines.
  As the Blood Infection spreads, the Player receives new Benefits and Penalties, ranging from reduced Skill Experience to fortified Carry Weight; reduced Damage Taken to Increased Damage Dealt.
  Infection Mode is the prerequisite to becoming a Vampire, and whilst it can be skipped through Death or Suicide, it offers a mid-stage gameplay, where the Player is required to balance the risk of becoming a Vampire with the benefits the Blood Infection offers.
  
• New Vampirism System.
  Skyrim’s Vampirism system is completely overhauled when Darkness Eternal is installed.
  Player-Vampires now possess a Blood Meter and a Starvation Meter. These two Meters represent how much Blood the Vampire has left, and how Thirsty they are; and it is from these two Meters that the Vampire’s total power is derived. Known as Vampiric Efficiency, this total power directly contributes to the Vampire’s Benefits and Penalties, and determines just how strong the Vampire is. A well-fed Vampire will receive greater Benefits and lesser Penalties than a Vampire with little Bloodand high-Starvation.
  
• New Vampire Powers.
  Unleash fearsome new Vampire Powers, including Faster Sprinting, Higher Jumping, Shape Shifting, Teleportation, unleashing a pack of Wolves and more. Stalk your prey over long distances with Predator’s Senses, or claim Dominion over their Souls (includes Named Soul-Gems for NPCs).
  
• New Feeding Methods.
  With Darkness Eternal you can choose to Sip Blood from Sleeping Victims, and restore only a small amount of your Blood Meter; or choose to Drain them completely to receive more Blood. Alternatively, Harvest Blood to create your own Blood Vials which can be used to sate your Thirst on the go. Victims’ Health degrades when they are Fed upon.
  
• Sun Damage.
  Beware the harmful effects of the sun! With Darkness Eternal, Vampires take Health Damage when exposed to direct sunlight, and the amount of damage taken is factored based on the current weather conditions (Cloudy, Raining or Snowing), and whether the Vampire is submerged or not.
  
• Water Damage.
  Be careful in the water! Vampires who are immersed in water will now take Health Damage.
  
• Updated NPC Vampires.
  But it’s not just the Player-Vampire who gets some new benefits. NPC Vampires receive their own versions of the Player-Vampire’s Benefits and Penalties, as well as overhauled Loot Lists, and new Death Effects.
  
• Find the Relics of Arkay.
  Hidden across Skyrim are the bodies of five Priest of Arkay, each carrying a rare and powerful Relic to use in your fight against the Vampire menace. Find all five, and become the bane of Vampires everywhere!
  
• New Consumables.
  Utilise new Consumables such as Blood Vials, Empty Vials, Fine Vampire Dust, Tomes of Vampiric Lore, and more…

Because there is a lot to read, please see the Official Tumblr http://darkness--eternal.tumblr.com/for full-details of all features and currently-implemented functionality.