If you're not caught up in the lore of the series (or are indifferent to the story), you're going to have a great time. A lot of gamers got caught up in the pre-release hype campaign at the time and imagined that the game would take a different narrative direction than it did. A lot of the irrational Halo 5 hate was spawned from this.
IMHO it's a fantastic game. The gameplay in the SP campaign is sublime. It's actually better on repeat playthroughs. As much as I disliked the squad aspect initially, I absolutely love it now. The combat sandbox is fantastic. Now that the shine has worn off of Doom for me, I think that I might hold Halo 5 in a higher regard from a gameplay perspective. I've certainly returned to Halo 5 more often since.
I've been following the series since it's launch on the OG Xbox and whilst Halo 5 wasn't the new Halo story that I wanted, I still consider it to be amongst my favourite games of this generation.
That said, I still feel that 343 genuinely don't understand the original appeal of Halo. The original game was viewed entirely through the eyes of the Master Chief, while a sexy half naked AI girl whispered in our ear and guided us in our "great journey". On top of that, we were going on an adventure to an uncharted world, seeing something completely new and we had a fantastic enemy to fight and an ancient history to uncover in our attempt to overcome adversity and circumstance. Mixed in with that was a brilliant and grounded combat and physics sandbox. That is an ULTRA SIMPLE formula to follow that is easy for any professional creative (worth their salt) to reproduce. Yet, 343 -with their Halo 4/5 team- seem to be completely ignorant of what made the original game a cultural icon that a majority of consumers could find appeal in. They seem to be transfixed on furthering a Bungie narrative that was already headed off in the wrong direction. If I was the game director at 343, I would have scrapped everything, gone back to basics, looked at what made Halo CE a success and gone "how can we make a 2018 version of that"? Because it's what "everybody" wants (*everybody = mass consumer appeal). Hell, if they just copied the Halo CE formula and dupicated that in the Halo 5 engine (+ any currently trending game mechanic), they'd be onto a massive hit. The dots are there, they just needed to fill them. I'm surprised that with all of the money that MS is throwing in their direction that they can't achieve a simple objective.