Sven is a versatile melee strength hero capable of being played as a carry or a support thanks to his ability to provide utility to the team and huge DPS largely independent of items.
With a potent AoE stun, an oft-underestimated aura ability, and an ultimate that has the ability to more than double his damage he poses a large physical threat even if played in a support role.
Skills
Storm Hammer is skilled and maxed first. 1-2 early points in Stats are taken to allow you to use it more frequently.
Great Cleave is skilled and maxed last.
War Cry is usually skilled at level 4 and is maxed second.
God's Strength is always skilled (levels 6, 11 and 16).
Items
Starting Items: Courier and/or Observer Wards, Tangos, Healing Salve, Gauntlets of Strength, Iron Branch.
Early Game: Flying Courier, Observer Wards, Boots of Speed, Magic Wand.
Core: Arcane Boots, Blink Dagger.
Luxury: Drums of Endurance, Vladmir's Offering, Aghanim's Scepter, Black King Bar, Medallion of Courage, Heaven's Halberd, Pipe of Insight, Assault Cuirass.
Situational: Soul Ring (early game mana access), Urn of Shadows (roaming), Mekanism (core if no one else purchases), Necronomicon (pushing).