Having quickly scanned through it, I will have to say, it is a gorgeous book. There's a huge amount of art, some of which we've seen before, but a lot that looks to be new. Also the scales on the cover of the book are raised, giving it a nice 3d feel when holding it.
The first section is on dragons in general, with basic stuff like anatomy, life cycles, hoards and the like. It also has a section on dragon gods, with Bahamut and Tiamat getting four pages, Sardior two, and the other dragon gods all given a quick run-down on two further pages. It's interesting how, even despite maintaining some Fizban's lore such as the First World and the (possible?) destruction of Sardior, the draconic deities are considered outright gods again, and not just powerful dragons as in Fizban's. Then we get into the dragons proper themselves, with each chromatic and metallic type getting six pages, gem dragons getting four pages for each type, and then a big chapter covering a whole slew of other miscellaneous draconic creatures, from kobolds and draconians to shadow dragons and dracoliches, each getting one or two pages. The final section details 30 individual dragons of note, combining old favorites as well as ones I haven't heard of before, each getting two pages. Good ol' Themberchaud is there, giving us a little bit of lore in how he moved from Gracklstugh to his own lair, with his movie appearance getting a bit of a nod.
Overall, it doesn't add much to D&D dragon lore, although it does consolidate it all quite nicely. But there are new things sprinkled here and there (such as, as I mentioned, the rumor that Sardior might have survived, and Themberchaud moving to a new lair). So if you're just looking for lore, well, it basically doesn't go much beyond what was in Fizban's. But... it's 200+ pages of lots and lots of really amazing dragon art, which, obviously, as a coffee table book, is supposed to be its selling point anyway.
(But still no weird, but traditional, chromatic or metallic dragons like yellow or steel. That would be my only complaint, and that's extremely minor).