Curious why you hated Halo 4's multiplayer so much? Some of the map design was really solid - I enjoyed most of them (Ragnarok, Exile, Haven, Adrift, etc.). The weapon and vehicle upgrades were a nice addition to freshen it up a bit. They got rid of some of the issues with Reach - bloom in the crosshairs, annoying abilities like armour lock, etc.
A lot of people seem to tout Halo 5's gameplay, movement, and multiplayer as being the "best since Halo 2" but I really don't see it. I've put in dozens of hours into the game, and while I appreciate the tweaks and changes made, it didn't hook me in as much as previous Halos. I even gave it another shot when the custom game browser came out, which breathed some new life into the game, but it still didn't have the staying power that the previous games did. Some of the changes felt like they were just trying to emulate Call of Duty, like aiming down the sights. To me, the franchise has been on a steady decline since Halo 3.
I feel the opposite, it was Halo 4 that went chasing COD, and Halo 5 that thankfully dragged things back on track.
Halo is about players starting matches on even footing, with the same weapons and skills at their disposal, and then earning more powerful weapons through map knowledge, communication, positioning, and great combat skills (shoot, grenade, melee... the holy trinity).
Halo 4 added garbage loadouts, awarded weapons on maps as f***ing killstreak rewards that could be called down anywhere... and to ‘balance’ that, they made the weapons you called in random. So when you get cross-mapped body-shot killed by the Promethean sniper, it wasnt cause that guy or his team earned it, RNG just smiled in his favor.
The weapon sandbox was also hot trash. Nothing was balanced, and 343 spent the entirety of Halo 4’s lifespan spinning plates trying to nerf and buff, but it was too broken from the word go to be salvageable. It was a disaster, and the population drop off in Halo 4 was the largest and fastest of any Halo game ever made.
With good reason. Halo 4 is shit. They tried to chase COD, and made a game that was worse than both any Halo ever and any COD ever. So instead of choosing to play a bad COD knockoff mashed into a Halo wrapper, everybody including Halo fans figured they as well just play the real deal rather than sci-fi CODLite.
Halo 5 was a huge return to form as far as multiplayer design. They abandonned loadouts, put weapons back on the maps in fixed spawn placements, rebalanced the sandbox so every weapon was viable and added a mobility suite to improve verticality and game speed, with abilitiew that every player had access to from spawn. Yes, they added an ADS option, but it was purely visual, aiming down sights did nothing to improve the practical accuracy, range, reticule-friction of any weapon. It was purely included for player comfort and could be ignored by any long-time Halo fan.
Halo 5’s failings were a lack of truly excellent maps and a lack of modes. The big bet on Warzone as a replacement for the BTB maps and modes was a bad bet. Which sucks. But the actual moment to moment gameplay in Arena, if you like pure, competitive Halo, is the best the series has beem since Halo 2. If you’re into more casual stuff like Fiesta or whatever, yeah, Halo 5 wasnt going to please you. They had to refocus on the fundamentals after Halo 4. Give me more of that with better maps and more modes and Im happy.