This has got to be the most complicated NES hack to date. A group of Japanese rom hackers recreated Final Fantasy X using the Final Fantasy 2j rom as a base. All of the graphics have been scaled down to 2D, but they still look impressive with the NES limited pallette. Cutscenes in the game have been reworked, not eliminated.
For instance the underwater scene between Yuna and Tidus still exists.
http://www.usamimi.info/%7Eff10fc/pc/gif/1_649_1.gif
The battle system has been recreated too. Limit breaks were added along with button presses for Auron’s Bushido attacks. The magic system has been reworked from the ground up to include more spells as seen in FFX.That would already be impressive as it is, but now imagine this. The entire sphere grid and the Blitzball mini game are also in the rom. It really is a 2D version of Final Fantasy X!
Check out the Japanese site http://www.usamimi.info/%7Eff10fc/
see the screenshots http://www.usamimi.info/%7Eff10fc/pc/scene.html

For now it's only in Japanese, I hope someone will take the effort and translate it.