I agree with a lot of what you said, even though I did enjoy Halo 5. Even though I have been really invested in Halo's story in the past, I tend to take CruelLEGACEY's view in that it doesn't have to be about anything. Halo 5 does exactly what it needs to in its story; it gives us a logical reason to go see cool places and do cool things. Should there be more? Yeah, probably, but it was serviceable.

: Even if we somehow accept this relationship between the Chief and blue team
: that we are TOLD exists (but not shown), then it is still pointless
: because it doesn’t manifest during the story. If you are going to
: establish a strong relationship like that, it needs to be in service of
: the story. The relationship needs to be tested or utilized in service of
: the theme. It needs to be there for a reason. The reason in Halo 5 is so
: that your co-op partners have someone to play as, and probably as fan
: service as well (which will be covered later). Basically, not only are we
: not shown the relationship, it doesn’t really have an effect on anything
: either.

We ARE shown the relationship, though, in a very, very clear way. They don't let the Chief go off by himself; they risk their lives by going with him, and whatever potential retribution from the UNSC that may come with it. That speaks volumes. So the fact that they are with the Chief the entire time is a very clear indication of their relationship.

: We have the same problem with the rest of Osiris. Buck is the most
: perplexing, since no explanation is given as to why he’s here, why he
: became a spartan, or what his stake in all this is. Did the comic books or
: whatever cover it? Too bad, I don’t give a shit, and now I’m drawn out of
: the story wondering why he’s here. You could have exactly two characters
: and still have the plot and story be the same: Locke and Chief. The rest
: of Osiris and blue team does nothing. Having them back is what people mean
: when they say Halo 5 feels like fanfiction.

Buck's transition to the Spartan program was covered in an extremely fanfiction-esque novel (in which Buck apparently knows every single person from the Halo universe ever; it's seriously awful), but I can definitely see how that would be off-putting to see Buck in Halo 5 without the knowledge. However, I don't think it's hard to imagine him becoming a Spartan given what we already knew about the Spartan IV program.

: With regards to Locke, I think it goes without saying that the story that was
: marketed to us would have been much better than what we got. Locke is a no
: nonsense, by the book, follows orders kinda guy who did some nasty stuff
: for ONI, or so I’m TOLD (not shown). So right there that’s in direct
: opposition to “No Sir” Master Chief. Groundwork laid for a great conflict.
: The major problem in the game was that there really wasn’t a conflict.
: Locke and the Chief are basically on the same side throughout the entire
: game. This of course makes their fight completely baffling and off
: emotionally. Sure his mission is to bring the Chief back, but why is that?
: Why didn’t Lasky just tell Locke to warn the Chief and make sure he’s
: okay? That’s what the old Lasky would have done.

Locke was an extremely weak character, I can agree with that. He's just a boring yes man and completely ignores Buck's prompts at conversations that could have shown us his character more. Also, you put my finger on what bothered my about Lasky in Halo 5. I feel like from what we've seen of him before, he would have helped in the Master Chief. .

: Cortana - As many people have pointed out, her behavior is completely out of
: character, and he obsession with protecting the galaxy using force is
: never been a part of her personality. If 343 wanted her to change, they
: need to give her reasons to change, and show that happening! Remember in
: the 5th Element when Leeloo is flipping through human history, and sees
: cruelty, war, genocide? She asks why she should save a species who does
: such savage things. Maybe when Cortana enters the domain, she sees all the
: shit that ancient humanity pulled (which I only know because I read online
: summaries, it’s not in the game), and realizes they’re actually the threat
: to the galaxy, and that’s why she wants the guardians? You know, make it
: motivated somehow?

I feel like her behavior being so out of character is very intentional, and huge indication that that IS NOT Cortana. Something obviously happened to her, and we'll get the story in Halo 6. Halo 5 was obviously just a large setup for that.

In the end, yes, it could have been better, and the trailers and Hunt the Truth painted a vastly different picture than what we got, but it served it's purpose for gameplay, and it certainly changed the Halo universe in large ways, which I like.