First of all, I don't yet have a copy of the new Dungeon Master's Guide for the updated 5E D&D. I'm poor and will have to wait until it can be fit into my budget. So, all of this is relying on the reports of others, first impressions, reviews, and so on.
The big changes have already been noted, being mostly some name changes that appeared on the map that was released to the public a few months back. The Scarlet Brotherhood's peninsula was renamed Shar, various tribal and "barbarian" peoples were given their proper endonyms to replace the exonyms that had previously appeared on the map, and sadly due to legal issues in the real world, the land of Blackmoor was renamed "Arn". Specifically, the Plains of the Paynims were renamed Plains of the Ulakandar (that should be "Uli", as Ulakand is a caravan town in the region rather than an ethnonym), Tiger Nomads are now Chakyik and Wolf Nomads are Wegwiur, the Rovers of the Barrens, while still called that in the text, are listed on the map as the Hunting Lands (which is correct as the name of the territory). The Frost, Snow, and Ice Barbarians are given their local names of Fruzti, Schnai, and Cruski. For some reason, though, the North Province of the Great Kingdom has been renamed to the cumbersome, ugly, and out-of-place "Aerdiaak", which doesn't seem to serve any useful purpose. I will certainly be altering that name at my own table for what the locals sometimes call it, and most people will call it the North Province when they need to differentiate it from the rest of the Great Kingdom.
In addition to renaming the peninsula on which the Scarlet Brotherhood stands, which as I've said in various places seems like a good thing to me, they've also chosen to rename the organization as the "Scarlet Order", which just doesn't roll off the tongue properly. In general, I'm not doing that, though of course as always it's nice to have alternatives available so that some NPCs might say that instead. Sorry, but ideologically racist, slaveholding supremacists sometimes might also be patriarchal in their terminology, and I see no reason to change that.
When discussing the Pomarj, it seems that the new writers are choosing to de-emphasize the fact that the peninsula is overrun by humanoid tribes and emphasize that they are acting as bandits and brigands. I'm mostly okay with that, though I do think that it's important to pay attention to the history and fallout of the Hateful Wars that led to the situation there. My general impression of the Pomarj at this point is rather like the Paul Verhoeven movie, Flesh + Blood, with bands of armed brigands and bandits, both human and humanoid, swarming the region and fighting each other over booty, slaves, and strongholds.
The writers have included three main lines of conflict that a given game could include: the rise of Iuz the Evil being the most notable, but also an entirely new conflict of the "chromatic" dragons (red, white, blue, green, black) being stirred to conflict by Tiamat from her home in the Nine Hells, where she is currently trapped. I forget which of the original conflicts is the third they've included, but it could be anything, such as the Drow and the Giants, the Scarlet Brotherhood and the Slave Lords, or the decline of the Great Kingdom under demonic influence among others. [Edit several hours later:] I see that the third conflict is Elemental Evil, which to me is already closely tied to Iuz, Zuggtmoy, and the Drow/Giants plot. I think that they would have been much better off treating the Scarlet Brotherhood, Slave Lords, and Wastri as the third conflict. Oh, well, missed opportunities are not unusual for the modern WotC/TSR/Hasbro conglomerate.
Most importantly, from my perspective, the new material adds notes on the cultural differences of different regions of the Flanaess, giving overviews of the way things are done in the West, East, North, and so on. That is what I want from a product like this, as to me the information contained in the Folio and Gold Box editions of The World of Greyhawk is most important and supersedes other sources, but new information helps to continue to flesh out the setting. I don't much care to see non-Oerthian types like "Aasimar" incorporated into the setting, as is done in the case of at least one leader, and would much rather they'd left that information alone. Changing a Viscount to a Viscountess here or there, as is done in Verbobonc, is a reasonable change, but I think that such things can be kept as they are or changed with no real repercussions to the setting so it should have been left up to the DM. This is especially true since the setting is supposedly included as an example of shaping D&D to fit a specific setting.
In the end, it seems like a reasonably worthwhile product even if it does do some things that seem only to make Oerth more like Toril rather than letting it flow with its own character. I'd strongly recommend getting at least a PDF of the Gold Box or Folio editions, or better still both, as a guidestone to the original shape of the setting, allowing the DM to adopt any changes knowingly and mindfully.