Sonic 2: Delta

Sonic 2: Delta is one of those rare hacks that is actually better than the original game. The original zones, with a few exceptions, are untouched; this hack restores zones that were cut during development.

While two of these zones (Wood and Hidden Palace) are available in the prototype ROM floating around the net, they’re in an unfinished and nearly unplayable state. One zone, Dust Hill, was restored based on a single mock-up screenshot; Winter Hill was based on an interview. Even Casino Night, which received a makeover since its beta state, has been restored to its former (very pink) look. The only zone that is incomplete in this hack is Genocide City, which is merely Chemical Plant with a different background and palette. Enemies from early revisions have also been restored

In addition to restoring cut zones, the hack adds a few new features: The ring counter now shows how many rings remain in a zone, the level select menu has been updated to allow access to the new zones, some Sonic 3 graphics have been ported, and even Knuckles has been ported from Sonic & Knuckles!

This is one of those hacks that simply must be played, its only flaws are the somewhat amateur-feeling level designs for the new zones and the fact it does not work on the real Genesis hardware.