So, it looks like something if a follow up to the previous BG DM's Guild product, although this one would be just fine to use on it's own, especially if you're adventuring in the Baldur's Gate or Amn areas. But even if you're not, there's still a lot in there that can be useful for any campaign, especially lots monster and NPC stats (still in the old format, but that's no huge deal. I wonder if they'll update the PDF with the new style as it's official).
The most notable thing are all the stat blocks. Lots of BG game characters with stats (many carried over from the previous product), including Jon Irenicus and Bodhi, both of whom are suitably high-CR foes.
The monster section has a lot of monsters, both general and FR-specific, that haven't been updated to 5e yet. There's a nice selection, although the phaerimm seem to be a bit weaker than in earlier editions (I'll have to take a closer a look at that later). Gibberlings, tasloi, sirenes, bebeliths, and demodands are all here, among others. Again, many, but not all, were in the previous product, but this makes them more "official".
But the Campaign Foes section - wow! Several big-name D&D creatures now statted up, including Baalzabul, Mephistopheles, Pazuzu, and more. There's even two forms of Bhaal!