Blood magic offers a dearth of ways to go through Minecraft, and can offer arcane methods for most tasks. Power gen? Try the Lava for Lifepoints method. Armor? Why yes please! A full set of enchantable armor that doesn't degrade and sacrifices your stored LP in exchange for damage taken. Travel? Air sigil allows flight, and is fast enough that the terrain won't render under your feet.
Couple that with over two dozen rituals ranging from the mundane (summon a storm, change day to night) to the unbelievable (want a meteor? You can have one.....) there's a LOT that this mod gives to the player.
(and ingame documentation would be neat, but I'm happy that WayofTime is continuing to provide more and more content instead.)