I agree with most of your complaints but I think you're missing the mark, and I can't quite put words to why. I liked everything about the game better than Halo 4 except Cortana, still having a bad villain (also Cortana), and the occasionally hamfisted dialogue, especially when it's expository dialogue (where sometimes it seemed a little forced and sometimes it seemed inorganic in delivery).
I also contest that every good story can be summed up in one sentence unless you allow run-on sentences and/or sentences with long lists, or just use the most generic milquetoast description possible like "it's about life".