As much as the Grimoire material not being in the game is bad, I have to hand to the writers, and now more than before.
There's stuff that goes with and enhances the story in the game, which has been talked about a good amount, but what I'm finding more and more is a lot of it doesn't really fit into the story proper but does dovetail nicely with some weapon descriptions, which are in the game and in some cases also in the Grimoire, and sometimes it dovetails with bounty and patrol mission text.
On top of that, and on top of the interesting tidbits and funny tidbits and short stories, there are implied stories and events that are becoming evident now that I've unlocked and read a lot of the cards. I also respect the... boldness, I guess, of not explicitly telling the story of certain things. You see stuff about Pahanin, for example, and if they told who he was it would be like "OK, that's that guy and now I have his gun; what of it?", but there are all these bits and pieces, it feeds this sense of things and people having legends. I don't think there's much talk of ancestors and descendants, but there are connections between people and places and things... I wonder if there's enough there to do something similar to the Lord of the Rings family tree.
Off the top of my head:
Dredgen Yor is tied to Shin Malphur, and Dwindler's Ridge, and The Last Word, and to Thorn, and thus to the Hive (and also what I believe to be the most oblique Marathon reference yet);
Pahanin is tied to Kabr and Super Good Advice, and Kabr talked about the Vault of Glass, and I think he died at the Battle of the Twilight Gap, so those are connections to those places (and that Crucible map and raid) and to the Fallen and Vex;
several historical figures, some of them Guardians, are tied to certain philosophies regarding the Darkness-- one of them is Ulan-Tan, and you can buy a Warlock bond that has a holographic replica of his burial ring, and one card talks about his followers causing issues for the Consensus (the leadership of the City);
another historical figure, a Guardian, I forget which, relays information on the Black Garden (and the Vex in general?), which they say came to them after leaping from the Shores of Time, linking that person and those two places, and indirectly linking the places to each other;
a Titan who fought at the Twilight Gap (not necessarily the battle with the Fallen) is implied to have talked to the Ghost that provides a post-mortem report on the Cabal;
a series of cards on the Vex describes a team at the Ishtar Collective studying a Vex specimen who turns out to have been studying and simulating them in turn, prompting them to bring in something the specimen can't simulate-- a Warmind-- to help their virtual selves (which may be their current selves), tying Warminds in general and that one in particular directly to the Vex, Venus, and the Ishtar Collective (and tangentially to Clovis Bray, if you want to reach for connections, because one of the researchers mentions them);
the Speaker regularly (always?) sells a class item called Deep Stone Crypt, and there's a card ("Legends" under Legends & Mysteries) that discusses the Deep Stone Crypt, but the class item's description says it depicts the subroutine (the infamous subroutine, as it calls it, which is a very interesting choice of words) that seeded the first Exo consciousness, while the Grimoire card describes it as a place that Guardians apparently dream about regularly and see as their birthplace-- I'm not sure what to make of that... since the place is implied to not be real, it's a logical construct in sort of the same way a subroutine is... the card could be referring to Exo Guardians or Exos in general, but I think the card is referring to Guardians and not Exos because it talks about being buzzed, slang for being drunk or "almost drunk".
What do you guys think about the Grimoire's expansion of the narrative and how it ties back into the game (and my thoughts on charting connections, which ran a little long)?