With this tier you get the Basic House, the Village Battle-Set, the Hobgoblin Outpost, the Town Adventure Set, and the Cities Mega-Set. This tier includes all stretch goals (other than the bonus buildings on the Cities and Citadels Tier).
This tier gets you all of the lower tiers including stretch goals, PLUS the Castle Walls. This tier also unlocks certain additional buildings based only on HOW MANY PEOPLE BACK THIS TIER. These are NOT stretch goals based on total funds raised -- the unlocked buildings are only for the Citadels backers.
At 125 Citadels backers, the Hobgoblin Citadel Walls are unlocked
At 250 Citadels backers, the Human Castle is unlocked
At 350 Citadel backers, the Citadel of the Hobgoblin King is unlocked.