Earth Spirit is a melee strength ganker and teamfight hero that is able to be played in one of a number of roles, from support, to offlane, to mid.
Warning: Earth Spirit has a notoriously high skill ceiling!
Skills
Boulder Smash is usually skilled last but maxed second.
Rolling Boulder is maxed last but is often skilled once early on for use as an escape mechanism/positioning tool.
Geomagnetic Grip is maxed first.
Magnetize is always skilled (levels 6, 11 and 16).
Items
Starting Items: Tangos, Healing Salve, 3x Iron Branches, 2x Clarity.
Early Game: Boots of Speed, Magic Wand.
Core Items: Arcane Boots, Mekanism
Luxury Items: Force Staff, Scythe of Vyse, Heaven's Halberd, Crimson Guard, Ghost Scepter, Shiva's Guard, Veil of Discord.
Situational Items: Observer Wards/Courier, Bottle, Boots of Travel, Blade Mail, Pipe of Insight, Necronomicon.