I was thinking about the fan made games that are part of an existing series. Some look OUTSTANDING. Here is a list of some of the ones I could find.
Sonic the Hedgehog
Sonic Before the Sequel
http://sonicbts.webs.com/
Sonic After the Sequel
https://sites.google.com/site/sonicbtsbooth/
Mega Man
Mega Man Revolution
http://megamanrevolution.com/
Mega Man Unlimited
http://megaphilx.com/?page_id=26
Mega Man Triple Threat (thinking this one is dead)
http://stealth.hapisan.com/MMTT/
Street Fighter x Mega Man
http://www.capcom-unity.com/mega_man
Mega Man X
Mega Man X: Corrupted
https://www.facebook.com/JKBGames
Mega Man X: Eclipse
http://forum.starmen.net/forum/Fan/Games/Megaman-X-Eclipse
Metroid 2
Project AM2R (this is a remake, but looks amazing)
http://metroid2remake.blogspot.com/
Let me know of others you are watching.
Sonic the Hedgehog
Sonic Before the Sequel
http://sonicbts.webs.com/
Sonic After the Sequel
https://sites.google.com/site/sonicbtsbooth/
Mega Man
Mega Man Revolution
http://megamanrevolution.com/
Mega Man Unlimited
http://megaphilx.com/?page_id=26
Mega Man Triple Threat (thinking this one is dead)
http://stealth.hapisan.com/MMTT/
Street Fighter x Mega Man
http://www.capcom-unity.com/mega_man
Mega Man X
Mega Man X: Corrupted
https://www.facebook.com/JKBGames
Mega Man X: Eclipse
http://forum.starmen.net/forum/Fan/Games/Megaman-X-Eclipse
Metroid 2
Project AM2R (this is a remake, but looks amazing)
http://metroid2remake.blogspot.com/
Let me know of others you are watching.