Seeing the ToC has me even more hyped than I thought I would be for this.
Items of interest:
20 (!) pages on the deities of the Realms, including a sidebar on the Mulhorandi gods. Much more than I expected; obviously we're going to get the main ones at least a bit of detail and summaries of the rest. If I remember right, this mention of Mulhorand is the first real indication that that area is back after the... misfortunes of the 4e version of the setting. I wonder how much detail the non-human pantheons will get, and if we'll get at least a run-down of the monstrous deities (there were lots of mentions of monstrous deities, including FR-specific ones, in the MM, and it would be nice to see an extended table).
15 pages on the Lords' Alliance, 8 on the Dwarfholds, 7 on the Island Kingdoms, 26 on Independent Realms, and 4 on the Underdark. That last seems... a bit low. Are they going to just refer people to OotA for more detail? 7 pages for the Island Kingdoms seems a bit high just for islands along the Sword Coast proper, so I have to assume that we're going to get at least coverage for the Moonshaes, if not something on Evermeet.
I'm really happy to see the subraces and racial variants. When starting my OotA campaign, we were wondering about half-elf variants, and, here we go! Also - Aasimar! I know they are in the DMG, but now they will hopefully be street-legal, so to say.
And I can't wait to get into the new class options and backgrounds. Again, these would no doubt have been invaluable when starting the OotA campaign, and I may see players re-rolling or adjusting characters...