It mostly took 2 days for me (Normal or Heroic) but that might've changed now. Yes, it might've been short, but the whole adventure you have in those 8 hours it's enough to make the game feel longer. At least for me.
Eight hours is average for a FPS these days. Halo 4 could've been longer than that, I know, but it seems fine as it is. Never played Spartan Ops too, but I wish I could.
For Halo 5 it's great. You got bigger maps, multiple ways to tackle your enemy's balls, but at the same time it's not been used as an excuse for making the game 5 hours long. That's painfully short.
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In other news, it's not officially stated, but I've heard rumours that...
Spoiler
The game begins with Osiris killing Jul' and saving Halsey. Since the the last issues of Escalation (19,20...)will deal with this I'm sure it would be a fine primer. The 1st mission will have Osiris somewhere in Kamchatka (another start with someone falling from orbit
) , then 2nd mission with Blue Team (b-roll footage), then 3rd mission on the lava planet (footage from ViDoc, Meridian maybe?)....forgot....forgot.... 7th mission is The Battle of Sunaion.
In short, blood will be shed, flesh will be torn, and the E3 footage is from later on in the game.
