Halo 1-3, ODST and Reach had simple but engaging story’s that all complemented each other because they were set in the same setting, the final years of the Human-Covenant war and the discovery of the Halo rings. Halo 4 had an engaging story as well but it failed to properly execute some ideas, like the return of the Forerunners being a little underwhelming and the new cast being (mostly) less favorable than the one in the original trilogy. It also failed to inform the player about important plot points like; what is this ''new Covenant"? Why do they look different and why do they not speak English. Halo 4’s story had continuity errors but was still a great story for the experienced lore fan.
Halo 5 on the other hand is almost like a soft-reboot of some sort. Halo 5 completely detached itself from its predecessor that was already kinda detached from Halo 3. The result is a story that literally feels like somebody took characters from the Halo universe, added some new ones, and made a generic sci-fi story that has nothing to do with Halo. If it wasn’t for Bucks’ occasional references to ODST and Reach I seriously would have thought that Halo 5 was set in an alternate universe.Events of the original trilogy are never mentioned in Halo 4, and 5 (except for a few vague lines)