I think the World Axis cosmology was one of the greatest strengths of 4e (which edition I liked, though I also saw its weaknesses). However, it had one huge flaw- it made huge changes in the existing cosmology, which meant ongoing campaigns that had major planar elements were either encouraged to drop the current game or to not use the new cosmology. There is one infamous comment by the 4e designers when asked about ongoing campaigns, where they pretty well said, "Yeah, just drop them and start over", which... well... wasn't very welcoming.
Anyhow, the fluff in 4e was great. One of the big flaws in the early books (e.g. the 4e Monster Manual) was that they didn't include much story; they seemed to reserve that for the more 'fluffy' books. Later on, the Monster Vault corrected this with what is, in my opinion, the flat-out best Monster Manual type book D&D has ever put out. The lore was amazing, fun to read, deep, and well organized. Likewise, reading any of the planar sourcebooks, there was great flavor all through it. It was very obvious that a lot of hard work went on behind the scenes to put the "big picture" together before the lore for a specific small bit (e.g. giants) got written, so that the little pieces fit together pretty perfectly.
But the middle finger to long time campaigns was (I think) a pretty heavy blow to the impression that the World Axis cosmology, and the lore tied to it, made on people. "I can't use this with my campaign? Well, then why bother?"
It actually didn't take a tremendous amount of work to reconcile the Great Wheel and World Axis cosmologies, especially if you're willing to posit that both models are just that- models for sages and wizards to use in comprehending the planes and how they align and connect. And, for one example, it's not hard to change the pantheon from the Dawn War "generic" one for whatever your campaign already uses.