As Ruin Ghost's ability resolves, the targeted land is exiled, then immediately returned to the battlefield. The land that enters 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 tapped, it does so. (Otherwise it enters untapped.) If it has an "enters" triggered ability, that ability triggers.

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