Let's see...

Halsey doesn't have her glasses.

The Spartans don't have minders in the amphitheater scene, and Mendez is not apparently present like he is in the book.

Halsey calls her project "ORION II" instead of "SPARTAN II".

The scene where Halsey asks Deja "How many dead?" is not in the book.

The Covenant ship that attacks the Commonwealth is a lot bigger than in the book. (Not a huge fan of this change. The original illustrated the sheer technological gap between the UNSC and the Covenant by having a small Covenant ship totally outmatch a human ship the same size. Now it's just a big Covenant ship owning a smaller human ship, which isn't quite as effective at getting the same point across.)

The Spartans are using the Halo 4/5 models of the UNSC weapons.

There's apparently a stealth Elite on the Covenant ship at Chi Ceti.

I'm surprised they kept the human-size AI holograms thing from the book, since that bit of old lore has shown up in almost no visual media.