As Ruin Ghost's ability resolves, the targeted land is exiled, then immediately returned to the battlefield. The land that enters the battlefield is a different permanent from the one that left. Any counters, Auras, and so on that were affecting the old land won't affect the new one. Any spells or abilities that were targeting the old land don't target the new one. Whether the old land was tapped or untapped has no bearing on the new one.

The returned land behaves like any other land that's put onto the battlefield. If it has an ability that says it enters the battlefield tapped, it does so. (Otherwise it enters the battlefield untapped.) If it has an enters-the-battlefield triggered ability, that ability triggers.

The land returns under your control, regardless of who owns it.