After a few months of teasers and plenty of time on the public test servers World of Warcraft's Update 7.2.5 has now finally arrived to the live servers as well. The Tomb of Sargeras raid, however, is only going to be opening its doors on Normal and Heroic difficulty next week, on June 20th.
As for the changes and additions, Update 7.2.5 has brought with it a new scenario featuring Chromie, the end of the 3rd PvP season, Black Temple as a brand new Timewalking raid, class-specific mounts as a part of the Broken Shore campaign, as well as a whole host of balance changes. If you're interested in all of the details, and there really is a ton of them, you can find what you seek on the official website.
On the other hand, if you don't care about the specifics and only want a brief overview before jumping in headfirst, here's the recently posted "Survival Guide" video. It should get you up to speed on pretty much everything Update 7.2.5 brings to the table. Anyway, here's the video: