They are neglecting the entire Colonial Militia/Operation TREBUCHET story arc and the comment the officer's about a "Tier 2" civilisation didn't sound right because that's a Forerunner designation of development not a Human one. But I'm willing to let them stray to let them show what they really want to show us - their impressive CG, props and battle scenes.
This looks pretty good. I find it funny that this looks better than plenty of movies I've seen by directors *cough*Transformers*cough* I give these people props (and I would if I had some! Bad pun...) and I'm gonna mark this to watch on a day when I'm not working. Can't wait to see parts 3 & 4!