Update (Fri 13th Oct, 2023): It's been nearly two years since we first published this list, and a lot has happened in the meantime! The acquisition of Activision Blizzard is finally now complete, and therefore we should be getting a large batch of ActiBlizz games on Xbox Game Pass in the relatively near future.
That said, Microsoft has already suggested that it'll take some time for these titles to join Xbox Game Pass, and Activision Blizzard has confirmed that Call of Duty: Modern Warfare 3 and Diablo 4 won't be available on the service until at least 2024. It's previously been suggested that brand-new Call of Duty games aren't expected to start joining Xbox Game Pass until 2025 as well.
There's also no guarantee that Sekiro: Shadows Die Twice will join the lineup, as the IP seemingly still belongs to the developer of the title, FromSoftware. It'll likely depend on whether Microsoft can work out a specific Game Pass deal.
As for everything else? We're not sure just yet, but hopefully some of them will join Xbox Game Pass soon-ish!