I voted for GTa style. It's a bit painful to fight your way through multitudes of monsters only to discover that you really should have left it until later. The only trouble is trying to not make the "bridges" so obvious. The picket fences in Divine Divinity (Elven Burial Ground and Black Lake Dungeon) were a real cop-out. Perhaps a bushfire, flood, or other widespread event that doesn't rely on a bottleneck?
