I'm pretty sure I covered most of the issues in couple of threads and last time I was accused of beating a dead horse for repeating myself so at the risk of being accused of that once more, I'll mention a few fundamental and technical problems I have with the game off the top of my head whether that being from my personal experience or something that is community wide among a number of players:-
Firstly, the back-end design of the game is shambolic and makes way for unreliable and unstable central server connections. SHG are the only company in the franchise that users server-sided fetch data rather than having partial profile data stored locally. This means potentially long loading times simply connecting to the main server. You could get to the IWNet MP menu in 15 seconds on MW2 and in BO1 you could boot into it from starting the console. Xbox users in particular have seen excess loads in over 10 minutes. It's been reported and acknowledged but wont be fixed or improved.
Next up is embarrassing animation glitches where player models are doing 360's and walking off the map - this means that what you are seeing and what is actually happening is not aligned and can leave you at a massive disadvantage. This problem has never been seen before and despite being brought to SHG's attention; they have chosen to ignore it despite being a glaring issue.
HQ is not needed whatsoever. The game ironically ran much better when it was removed. It's only being retained in a bid to push supply drops. Until they add some purpose, it's not really required and not worth the excess strain on what already is a server savage title.
Other calamitous issues is team balance - I've been in matches where it's 4v8, 5v7 and one match I even spawned on the enemy team side. This simply should not be happening.
The netcode is simply woeful. The engine may be extremely old but the inconsistent way the data has been coded onto it demonstates sloppiness that you wouldn't expect from even amateur developers let alone a COD one. Bad netcode ruins the experience even if the connection is amazing. If the netcode and the connection is solid like you see on Overwatch; you get a perfect and fair experience.
Other issues I pretty much echo what is said above - 9 core maps is ludicrous. MW2 had 15 at launch. 3 of which were REMOVED from the game between the beta and the gold branch which means Activision are charging people on withheld content. Just because War is a new mode doesn't mean players should receive any less from the central aspect of the game. The first DLC contains 2 new maps (lol) 1 remake (that was released last year as a remake) 1 war mode (not everyone plays War) and 1 zombies map (not everyone plays zombies) I got bored of the beta maps before release and that was 33% of the entire rotation. I hated 3 maps which was another 33% meaning I only had 33% maps that I enjoyed playing.
The points system is a mess too - 34 kills in DOM to earn the top killstreak and 10 for a bloody UAV? SHG changed this for the beta but then had to lie about a privately conducted poll to justify why they wouldn't chanage it in the main game.
No anti-cheat on PC despite SHG promising both VAC and manual review support. Developers lied again.
Restrictive loadout system.
League play is laughable.
Killstreaks are shite.
Pistol grips.
That's all I can think of off the top of my head. SHG didn't even want to make this game - they were making Advanced Warfare 2 before Activision told them to switch. Although I enjoyed the camapign and other parts of the game; it is clear it is rushed, incomplete and riddled with funamental flaws that I wouldn't expect from the brand these days. This is why it's being patched relentlessly rather than being improved and moving forward. I just hope it doesn't affect future developement as the more time they have to waste on this; the worse prepared they'll be on the next game which is exactly what happened with Bungie on Destiny 2 and why that game released with sod all content and depth.