I have compiled sales data for each title of the main First Person Shooter franchises to see how the genre is trending so far.
These are the combined sales for all consoles for each title:
Call of Duty: The franchise is trending down, Black Ops III kind of reversed the long decrease in sales started 6 years ago but Infinite Warfare sales reconfirmed the trend as it might not even reach World at War sales.
Battlefield: While the franchise is still decreasing in sales, it is now competetive against CoD. B1 is actually at 11.59M vs. 11.55M for CoD: IW. This is the first time a Battlefield game outsells a Call of Duty.
Halo: Since Halo 3, the franchise is also decreasing in sales. Halo 5 (4.71M so far) did not even managed to sell half of what Halo 4 did (9.81M).
Far Cry: This is definitely the healthiest FPS franchise and the only one whom its last release performed better than its previous iterations.
Killzone: While underperforming compared to the other franchises, Killzone games are quite stable, selling between 2.5M and 3M during the last 8 years or so.
Resistance: The franchise started really well in 2006 but did not manage to grow and finally died with really low numbers in 2011.
Overall we can say that FPS games are not doing so well. Sure, CoD and Battlefield are still doing great numbers in comparison to other genres but it seems the golden age for that genre is now something of the past.