I was actually contemplating how long each of the other campaigns actually were, atleast the first time of the playthrough.
Halo CE was really long, but that was also because I learned the controlls and so forth, it was a little more difficult then than it is now.
Then Halo 2, I played that through with a friend the first time, and we took it in an evening. So it wasn’t that long either, then again with a friend it was a lot easier.
I blew through Halo 3 the first thing I did. If I remember properly it landed around 8 hours, on heroic.
Halo 3: ODST then, no idea how long it took the first time. But probably around 10 or so hours due to me experimenting in New Mombasa, then again. Might cut off 4 or so hours due to the exploration and concentrate on just going forward in the story.
First time I tackled Reach was on Legendary. I didn’t get that done in a day, so time is a littlw bit iffy, but if I have to guess it probably felt like 10-12 hours.
with Halo 4 I blew through it in some 7-8 hours on Heroic the first day.
Moving on to Halo 5, start on legendary solo, complete it legendary solo. 8 Hours and 19 Minutes. Roughly the same time as previous games. Not speedrunning. However, seeing as it was Legendary and on solo, I’m going to say that atleast a quarter, two hours, would’ve been saved on an easier difficulty.
Now, I think it’s a short campaign. However, I think there are other contributions to that feeling. That feeling is that the story itself is so short and not actually much happens in it. MC has little screen time, most of the missions after Locke and MC knucklefight is a campaign stretcher till the point of getting to Genesis. The Warden is recycled time and again and basically most of the plot happen at the end of the game. We don’t progress that far in the overall story.
Heck, it feels like the 4 first missions of SC2: LotV progressed us farther in the overall story than Halo 5 did. Top that off with the fact that the 4th mission is the first “proper” mission when you actually get to choose where to be with upgrades and stuff.