King Colossus is a Mega Drive game made by Sega that was never released outside of Japan.
It's got some truly impressive programming and a great plot. However, it can be quite frustrating at times, although ultimately the difficulty level is rather easy. The music is excellent and the director did a fine job overall.
 
 

This is a very high quality piece of work, both in the hacking and translation departments. It was also the first dual-language (Jap/Eng) fan translation of a video game; the original Japanese script is intact and can be accessed by setting the country code to Japan, instead of USA (when using an emulator). That aspect was implemented mostly just for fun, but it does improve upon the original Japanese version in some respects (such as longer names and bug fixes).
 
 

King Colossus Jap-Eng Translation.zip

King_Colossus - Family Friendly.zip
This version is almost identical, just with the mild language removed, making it comparable to what one would have typically seen in games from this time period. This was the only time I ever did such a thing.

Here are some before and after screen shots. Not all of the changes are included. In particular, images of many of the various submenus in the pause screen have been omitted.
 

The low-quality compression makes some of the text look a bit blurrier than the source material.
 

Lower-case letters were not originally an option...	...neither were 8 byte names and the kana "VU".
The original would pad names to always be 4 characters.	This version permits names from one to eight characters.
Same picture as before...	...but this one demonstrates the dual-language feature.
Originally, all rankings were just a single-digit number.	Now an appropriate suffix is added.
There are two endings, hence two backgrounds.	Fixing some of the credits required new tiles.