Ok, as someone who is not Johns fan, not a Green Lantern fan, and barely interested in DC, I'm going to try and look at this from an outsider perspective, in terms of what Johns has done over nine years, both postive and negative)
-Completely marginalised Kyle Rayner as a character
-On the other hand, completely successfully rehabilitated a toxic character, and actually laid down a template on how to do so (ignore everything that has gone before)
-Pushed his creative vision for a character onto a film version that didnt need it, and as a result, saw that film totally tank.
-Created a rich and varied supporting cast that will almost surely be totally ignored by the next writer
-Built a franchise out of one character, supporting four well selling books.
-Supported two bloated, but high selling events
-Managed to rise above the stink of the DC relaunch, mostly by ignoring it and plowing on with the story.
I'm fascinated to see whose next. Be interesting to see, given the civil war at DC, Johns will probably have a say in it, which means Sterling Gates, or Tomasi, or Harras and DiDio's camp will win out, and it'll be Scott Lobell and Tom DeFalco.
Personally though, I'll bet the change in my pocket that Jim Starlin gets a go.