With all this talk about bad retcons and the whatnot, we do OCCASIONALLY get a good retcon, now I post this here so maybe the MK Team can get a good idea on how to make good retcons, but yeah... I know.... but anyway

Raiden being turned from crazy god who didn't give a damn to Protector of Earth:

While maybe crazy Raiden was more interesting, (not necessarily my opinion but some think that) but with all this Good vs. Evil battle coming up, Earth's warriors needed a mentor/leader and besides it makes more sense for the Gods to actually care about their world's safety.

The retcons in MKM:SZ:

Minor bits about Scorpion's family were retconned, but they served a purpose in giving him a rather interesting backstory, the only slightly confusing one is that Shang Tsung invites Sub-Zero personally rather than him being sent to assassinate Shang Tsung, but this could easily be explained.

(This one I've heard about, but it's not very well known) Johnny Cage dying from the Extermination Squads rather than at the hands of Kintaro in MK2: The story behind this is that I heard this soundclip which was meant to be an advertisement for MK3, a funeral for Johnny Cage is being held with Raiden giving the service and a woman (Sonya?) crying in the background, it mentions that he was killed by Kintaro. Then it goes "Mortal Kombat 3! It's not over! Not by a long shot!"

These in my opinion, are the only examples of good retcons in the storyline. (There's probably some I'm missing, but oh well...)