Exandria, like Greyhawk, Forgotten Realms, etc., is a standard D&D fantasy setting. It doesn't push the envelope imo other than the Divine Gate (which CR has abandoned), and it treats the PHB/DMG/MM like lego: you can fit any race, item, spell, or monster into the world seemlessly. I think this is a major plus for a DM who just wants to run a D&D world without the need to homebrew a ton (though you certainly can).
Each of the three sourcebooks has a very simple, straightforward style. Tal'dorei was built up in an
ad hoc, city-by-city way: if you're familiar with Matt Colville's "Running the Game", it was basically built that way (not on purpose I imagine, it just happened). As a result, Tal'Dorei's somewhat empty and very simple (good republic, elf city, dwarf city, wilderness). Wildemount is more interesting, it was designed and was intended to be more grey. It has four distinct regions (imperial west, mercantile south, monstrous/weird east, and wild north), but in the same world.
If I was going to summarize the setting, I'd say it's like this:
- Religion: Uses the PHB's Dawn War Pantheon with a few alterations here and there. There's a "Divine Gate" which prevents the gods from meddling on Exandria.
- Lore: Set 800 years after a magical apocalypse wiped out most of civilization. Lots of ruins to explore, lots of problems left over, etc.
- Factions: Each region has a number of distinct factions and there are a lot of great hooks for players to plug themeslves into the world.
- Gazeteer: Each region has its own little infobox with simple helpful details (demographics, gods, economy, etc.) Each sub-region within the Gazeteer has quest hooks for low, medium, and high level parties. A few NPCs are listed but nothing exhaustive: very table-ready.
- Sandbox: Funny coming from the massive changes in the third campaign, but the sourcebooks have some hooks for meta-plots if the DM wants them but it's also easy to just plop and play.
For criticisms, I'd say the homebrew is generally undertuned and I'm not a huge fan of the Blood Hunter or some of the game's subclasses: they're not bad, they just needed more of a community edit (understandable why that wasn't possible). A lot of small nitpicks outside of that as well, stuff like the Calendar (players never use the days it's just a bit too out there).
I think overall it's a fine setting even if you don't give a crap about CR. I think as a DM, if you want to run a sandbox but find GH/FR have too much baggage, but you also don't want to run CR, just get the Wildemount book and file the serial numbers off the names: it's good-quality scaffolding for a tried-and-true style of sandbox.