Zelda Outlands
The old world map has been completely overwritten by the new one. You are guaranteed not to recognize any locations from the previous game. All location of dungeons and secrets have been changed as well.
Secrets are now locked according to what quest youre playing. For example, the rock you push to find a dungeon wont move on the second quest, so you have to find a new entrance somewhere else in the world. The game allows each secret to be set to 1st Quest, 2nd Quest, both, or neither. So, many places where you can bomb, burn, push things and use the recorder are quest-specific.
Most of the monsters have new graphics (including all bosses) and some even have new colors.
There are 42 possible block, water & statue arrangements for the many dungeon rooms, and all but 3 are brand new.
Thats just a taste of what has been changed and how much work went into this hack!