I have to agree, looking at it retrospectively -
The good -
1. Great movement.
2. Solid weapons.
3. Solid audio.
4. WZ was fun but limited.
5. A few good maps in the small category.
6. REQs were implemented well and kept away from competitive play.
7. Firefight was eventually quite good but missing at launch.
8. WZ maps were pretty well fit for purpose.
9. Smooth and solid framerate that made responsive and cohesive gameplay.
10. Sustain was eventually good e.g. they updated the game years after release with major content e.g. Forge, Firefight, PC Forge etc.
The bad -
1. Waaaay too much focus on esports, 343 literally cut out the most popular modes of Halo 1-3, default radar 4v4 and 8v8. They split the game down the middle with pure esports vs casual WZ.
2. Maps were too focused on slayer and small sized maps, again they literally cut out light vehicles 4v4/5v5 type stuff near completely.
3. Fuck all objective focus, WZ's OBJ mode turned into a grieving session and basically the population fucked off. You can't affect gameplay when in large team sizes and it's not fun long term to match full squads. Games like Apex for example give you a core 3 man squad and you engage and can affect your game outcome and experience heavily.
4. Matchmaking and region support was utter shit, specially outside USA.
5. The late term updates for region support still favoured developer implementations over player controls and choices. Again games like Apex or Titanfall give full control to selecting your Azure regions. There is no excuse here 343.
6. Lack of content e.g. firefight took like 1.5-2 years to show up.
8. Sustain was shit for the first 6-9 months post launch.
9. Population, again especially outside the USA, was shite. Modes were left unplayable.
10. No splitscreen.
11. No LAN.
12. Lack of matchmaking filters e.g. maps and modes.
13. Too much geometry for multiplayer e.g. grenades get stuck in pipes or you walk into a small part of geo etc.
14. Breakout received a chunk of dev resources and failed, they should never have gone after yet another esports mode e.g. chasing CS:GO/COD faster TTK.
15. Forge was missing at launch
16. Then BTB was all forge maps.
17. All that great movement and complexity/flexibility given to players comes at the cost of randomness in engagements, the predictability of Halo firefights went out the window somewhat. This is more a sum of the parts problem e.g. grenade wall bounces, thruster, combo momentum. Comparatively games like Apex have these sorts of traits but they're character specific and you inherently identify the character and traits available to the engagement you're in (even to the point of calling enemy characters out to teammates when you see an enemy). With Halo 5 all the Spartans vary wildly visually and have the full gamut of abilities available at any moment, which gives rise to this randomness within each firefight. It sums up to being too much.
Honestly H4 and H5 basically turned their back on the most popular playlists from H1-3, 4v4/8v8 slayer social/ranked and 4v4/8v8 objective. They moved too far into esports for maps and modes, the movement and gunplay is worthy of keeping and pushed into you're just cannon fodder in WZ. It's a little to complex and lacks that clean identity and gameplay.
The biggest issue with 343's Halo is identity. The multiplayer has to support so much and it feels like it doesn't know what it wants to be exactly. 343 tried to define the split from esports/WZ and retain populations within, it failed. When you look at something like COD warzone or Apex or Fortnite or PUBG they support very limited modes but the core gameplay is tight AF, the characters and weapons and movement are very well defined and identified instantly during gameplay. Halo has lost this, especially with Halo 5. The core mechanics are there, 343 nailed that but it needs refining and clearly put into the right sandbox of quality maps and modes developed out of that gameplay loop.
This is the development hell 343 have been in for all of H4, MCC and H5. It's clear they're struggling to deliver an industry leading FPS hitting all the notes across the board e.g. campaign, multi and something new. Bungie's rule of 3 should apply here, focus on those elements. H5 had that clear design goal but executed it poorly. Hopefully Infinite has corrected this next attempt and delivering that trio.
Another area I was truly hoping to see out of 343's Infinite development is PvE content for Halo. I and my old regular Halo/Destiny crew would kill for Destiny/RPG-lite levels of sustain with Halo; such as RAIDS, strikes and public events/areas combined with loot and progression/customisation. The reveal not showing anything in this regard and no information on multiplayer has me seriously concerned with what is going on development wise at 343. Hopefully they pull a winning combination on the river card with this development game of Texas Hold Em, we haven't seen their hole cards yet. Please don't be bluffing.