Some of these might be hot takes, so bear with me. While I did play multiplayer for the original Call of Duty games prior to Modern Warfare, it wasn't enough to establish a good opinion.
• Call of Duty 4: Custom classes were amazing and the modern setting really refined the aesthetics. However, map design was lacking overall and a bunch of perks were rather useless, especially eavesdrop with the Xbox live party system.
• World at War: It took notes from Call of Duty 4 with the custom classes, along with some dark and heavy aesthetics. The tank maps were the worst arenas and there were still some perks and equipment items that were not useful whatsoever. The guns also sounded like crap.
• Modern Warfare 2: further refined custom classes with better perk placements and new streaks. The rest of the game was an unbalanced mess with deathstreaks, some bad maps, and horrible post launch support. Killstreaks were especially way too overpowered when they chained together, which basically made the game less gun on gun and more AI versus player.
• Black Ops: Greatly balanced game for the most part and good maps. Second Chance was annoying and my personal gripe involved the dumb noises made while reloading.
• Modern Warfare 3: The gun sounds were amazing, there were lots of streaks to choose from, and face off was incredible. Death streaks were even worse and the support strike package was abused with constant stealth bombers. Limited sprint was a terrible idea.
• Black Ops 2: Amazing scorestreak system and pick 10 was revolutionary at the time. Some of the streaks were too overpowered. Limited sprint still killed my thumbs
• Ghosts: Custom operators were pretty cool and maps having their own streaks/events were unique. The huge selection of perks were interesting as well. I didn't like the desaturated tone and the base maps were too big. Dual rendering scopes reduced the frame rate. Oh, and the IED spam with people abusing the amplify perk to listen in on footsteps was outrageous.
• Advanced Warfare: The game looked great, it played very fast, and the customization for operators and streaks were amazing. Supply drops restricted the armory and some weapon variants were too powerful.
• Black Ops 3: The game had a unique hero shooter vibe with some decent maps. Advanced movement was really slow overall and some of the operators had annoying abilities. Most of the armory was locked behind drops.
• Infinite Warfare: All of the maps were very good to play on and the advanced movement was fast and smooth. Supply drops still ruined the full armory, even with base weapons being unlocked by challenges. MKII weapon variants were a waste of time and were only implemented to make supply drops harder to acquire new gear.
• WWII: Restored the classic vibe of the series, along with the cool HQ area to hang out in with an amazing war mode on top of it. The game was really rough with custom classes, even after the April update. Also, pistol grip skins were a bad idea.
• Black Ops 4: Really solid multiplayer with some iconic maps. I didn't like certain weapons not having all attachments. 5v5 was awful and I felt the time to kill was a little too long.
• Modern Warfare: Pushed a heavier emphasis on realistic military aesthetics and introduced very good online features like cross play and no supply drops. However, a bunch of maps were horribly designed and reverting to the default killstreak system was terrible. No dead silence perk was also abysmal.
• Black Ops Cold War: Multiplayer was very fast-paced and the maps were pretty good. I also loved the faceoff playlists. The streak system wasn't good because they mainly rewarded gunstreaks over objective play, which is the antithesis of the original scorestreak model from bo2.
• Vanguard: I honestly liked the chaotic gameplay and Champion Hill was the best. Weapon customization was cursed and the game jumped the shark with the ridiculous sci-fi cosmetics. I wasn't a fan of combat pacings either because it basically gave an excuse for developers to make bad maps by filling them with more people to compensate. The game had terrible camos and people camping with LMGs with the piercing vision perk ruined everything.
• Modern Warfare II: The time to kill being fast was a benefit and toggling between kill streaks and score streaks was decent (but not perfect). I really like the camo system with every weapon having their own unique unlocks based on a variety of challenges. The maps were still terrible, timed perks were bad, and there was still no dead silence perk.
• Modern Warfare III: Much better movement and the carry forward system was pretty cool. Finally having dead silence aka covert sneakers was a godsend. I wasn't a fan of the higher health pool and it made balancing weapons more tedious than It had to be. Additionally, the remastered MW2 maps were mostly horrible.
• Black Ops 6: Omni movement was amazing and the game played really well overall. Some maps were not too great and the skins got a little too wacky (mainly the cell shaded Beavis and Butthead). Also, I hate camos being rewarded for only headshots. It was a regression from what MWII/MWIII did better.
• Black Ops 7: Even better Omni movement with some content being carried over via scorestreaks. Not a fan of persistent lobbies because you'll end up rejoining the same lobbies repeatedly. Open matchmaking is not very good because squads can dominate more often due to the weaker skill component not being able to be a proper counter.