>trimmed down mechanics in the name of easier fluff and create-your-own-content
While true, D&D has always at its core been designed to be user-friendly in this regard. So if it's easier to create your own content, that's a mark in its favor.
>ditched existing fluff in the name of giving you a sandbox
Actually it ties in far more closely to existing fluff. Forgotten Realms fluff, anyway, but that's not a bad thing; in any even this edition is if anything tied more closely to its "default (the Realms) then 3rd Edition ever was to Greyhawk or 4th was to their Points of Light thing. And again, D&D has at its core always sought to be fairly modular.
>ditching 'gamey' crunch and selling that lack of crunch as better for narrative.
Given how much that was called out as leading to broken rules, I cannot see how that is a bad thing.
>promised swathes of new content at release (re-done races/modular systems) that hasn't shown up
I was unaware of any such promises.
>nuked all archives of existing content and support to force uptake of new products
Nope. I can still find all the old 3rd Edition stuff on WotC's website, in any event. Dunno about 4E, because I don't care about 4E.
>almost opposite approach to power, from high fantasy to low fantasy and low fantasy to space fantasy
In a world with monks and rangers that can cast spells, I hesitate to call D&D "low" fantasy.
>has polarised the community
Oh, every Edition release since AD&D has done that.