See, just gonna throw this out there, but CoD is a pretty bad example of gameplay and graphics merging, and I'll explain this pretty quickly in a couple paragraphs. There will be no tl;dr, but if you're interested, read it.
Starting with gameplay, their core gameplay has remained relatively unchanged since CoD4, which is ok since it's found a good framework for gameplay, which has worked. However, the balance for gameplay has actually deteriorated heavily for the sake of "easy of access" and visual appeal. Kill streaks are the main example of this. Gameplay-wise, they aren't a bad idea. Rewarding good play is inherently a good thing. However, when you get killstreaks which aid in getting more killstreaks, you create a snowball effect, a game feature which is invigorating for the person getting the kill streak, not so much for everyone else. And I'm not saying this as a scrub who gets rekt in every game he plays. I'm saying this as the guy who would eviscerate the enemy and leave my team nothing to kill. It becomes too rewarding for the player who is already ahead, letting them get further ahead and ruining the experience for everyone else.
Secondly, in an attempt to counter-balance this from happening, they increased the efficacy of newb-friendly weapons, like explosives and shotguns, to try to give players on the receiving end a fighting chance. However, it's a double edged sword. The very weapons designed to make it easier for newer players to fight on par with veterans were incredibly oppressive to fight against if a veteran decided to use them. Instead of being great equalizers, they further exasperated the problem.
Lastly on the gameplay front, they have definitively shrunk the battlefield and changed spawning patterns to facilitate a skirmish style of gameplay, rather than a battle line style, which was last used in CoD4 and BO1. What this means is that, instead of spawning you roughly within the safety of your team's location, it will try to spawn you somewhere in between your team and your enemies. Which is, again, a gameplay style which benefits veterans more than newer players. The strength of a battleline style of play is that you never have to feel pressured into finding your bearings when you spawn, as you have reasonable expectations to be safe because you're surrounded by your team, and they have a definitive line drawn that they're holding against the enemy. However, in a skirmish style game, you have to quickly evaluate your location on spawn and adjust where you need to go instantly. A veteran will quickly get their bearings and get going like nothing happened. A newer player doesn't have the time they need to get their bearings. The battle will literally be brought to them in a couple of seconds, and there is no safe window to try to gather yourself together.
Now, going to graphics, they're still running on a modified Quake engine. What does that mean? Basically, they're using the same engine that they've used since CoD2 that's been modified for different features, like sprinting and killstreaks. What's wrong with this? It limits their graphics capabilities to the limits of the Quake engine, and a dated version at that. The majority of time developing is spent cheating the engine and hardware requirements to make newer looking graphics. In addition, CoD has some of the most blatant reused assets in the game. If you walk around in MW3, you will see models and textures being using from MW1. Heck, Ghosts used an entire animation set from the MW2 ending scene for their opening scene frame for frame. It saves a lot of money, but it looks like ass if you know it's there.
CoD is far from a shining example of a good merger between gameplay and graphics. It's a relatively stale franchise that's approaching EA Sports level of recycling.