You'll have to wait until Halo 6 if you're hungry for more of the Master Chief/ Cortana storyline, as Creative Director Josh Holmes has confirmed in an interview with Red Bull that there will be no DLC for the current Halo 5 campaign mode.

The length of Halo 5: Guardians campaign is nearly twice that of Halo 4, based on average playtime in user research testing.

While we’re always looking for new ways to expand the Halo universe, we do not currently have any plans to release future campaign content for Halo 5: Guardians.

The Halo5 campaign mode has been getting mixed reviews from news outlets and players alike. The prime source of grief seems to be the "same ole" style of gameplay, which is strange because Halo 4 was ripped apart for "not feeling like Halo". Damned if you do and damned if you don't I guess.

Personally I didn't feel that the Halo 5 campaign was all that long, in fact I powered through it on normal in around 4 hours. I like to get those pesky campaigns out of the way though, so I could see how someone taking their time and enjoying the sights/ looking for skulls would take much longer.