On a physical level, games show us stuff on screens and send sound to our headphones. We use the information from those two sources to respond physically via pressing buttons (digital) and moving the mouse (analogue). At that level of abstraction, there's only a handful of ways that you can make the process of see/hear info -> press button/move mouse difficult. You can:
turn the information into a puzzle about the "right" button to press or mouse motion to make
require sequences of buttons to solve the puzzle
require tight timing in those presses
And that's it.
A game like guitar hero, for example, literally shows you exactly which buttons you need to press and when. It takes the puzzle element totally out of the equation. The whole difficulty is the tightness of timing (you have to press the button on-beat), and the sequence patterns are difficult to perform physically.
In a 2D fighting game, in order to use a fireball, you might have to press s down, and then press d down, and then let go of s, and then press u. That's a tight sequence of button presses that you have to execute accurately or your fireball won't come out. The faster and more accurately you can perform that, the better you'll be. A fireball might be one small part of a larger combo. Maybe in order to successfully hit an opponent with a crouching medium punch into sweep combo, you need to press the sweep with 1 frame timing. This means that you have a 1/60th of a second window to press the sweep button, which resolves to ~17 miliseconds. So, after you press your medium punch, you need to press your sweep somewhere between 230ms and 247ms afterwards. If you press it 229ms after, you were too early and you don't combo. If you press it 248ms afterwards, you were too late and you don't combo.
In a game like counterstrike, an enemy will appear on your screen and you need to make a mouse motion that moves your crosshair on top of their head and then press lmb. If you move it too far, you'll miss and if you don't move it enough you'll miss. If you do it too slowly, they'll shoot you first.
In a game like chess, you need to interpret the information and then make a small mouse motion that drags a piece from one square to another square. Different small mouse motions have drastically different outcomes, and so the whole game comes down to puzzling out which mouse motion is the correct one.
In a game like WoW, you're presented with a ton of information on your screen about the state of a fight. Your health, their health, your cooldowns, their cooldowns, your resources, buffs, procs, etc. Then, you need to puzzle out which button you want to press next. Power Infusion, Void Eruption, Shadow Word: Death, Mind Games, and Shadowfiend are all available, and are bound to different buttons on your keyboard. To solve the puzzle and maximize dps (or win the pvp fight), which is the best button to press next?
So to WoW players, of whom the difficulty is in solving the puzzle, they look at New World and say "you just use your abilities and then spam lmb". The game looks way less complex because the info->which button puzzle looks extremely easy relatively.
New World players look at WoW players and say that their game is just about the puzzle and that there's no sequencing (weapon swap combos, precise mouse movements, baiting / outspacing people's ablities) and no strict timing requirements.
They're both right.