My deal-breaker is if the edition is not more enjoyable for me to play in and run than another fantasy RPG I am aware of. That's kind of it.
I can't say that I'm in the "Feels like D&D" boat at all, since what many people describe as D&D sounds horribly boring to me. My only taste of their definition of D&D involved me knocking down towers instead of going inside of them and making the DM throw away the adventure he'd wasted his evening preparing.
Give me the game that facilitates contemporary fantasy roleplaying as I envision it best, and I'm happy. Whatever edition of whatever game that may be. I don't do brand loyalty.
And I'm the exact opposite. I don't want D&D to be the game the represents the game playing fad of the moment, I want D&D to be well, D&D.
It's sort of like how the NFL wants to expand into Europe, possibly moving the Rams there full time (since they likely will be leaving St. Louis since we won't build them a new stadium).
What if it doesn't prove to be popular there? Should they make it more like European football rather than North American? Use a round ball, get rid of downs? The end result might be great, but it just wouldn't be North American football.
It just seems to be that so many people simply just don't like D&D and would be happier playing a different game, but instead they want D&D to become that other game.
Which then ironically, forces those that actually like D&D, to go to clones of past editions. And in this case, Pathfinder is doing well enough that it is taking significant market share away from D&D.
That's really the thing involved here - in the past, when D&D moved on, you pretty much had to move on if you wanted new products (beyond fanzines and the like). But now you don't - in Pathfinder's case, the product quality exceeds most of WOTC's output...and some of the OSR stuff is pretty nice as well.