The problem is that there is nothing to understand in QTE. You just get prompts showed in your face without context or idea what will they do. After slicing the tentacles part which is kind of obvious according to derpy vidyagame logic and which is easily the best part of that battle because it relies on actual mechanics and movement rather than prompt spam, you're left in the dark.
There is no cohesive interface or mechanics, so you simply have no idea what the fuck you're doing or what the fuck is happening, other than flashing prompts and pressing keys you're told to press.
Worst. Thing. Ever.
There are ruins that get destroyed right in front of you, forming a natural ramp that end right over the monster's head, which is half incapacitated at the time... and you don't know what the fuck to do?
What do you want, hookers pointing you do drop a bomb on his brain?
I really never got all the kayran whining, really.
The problem is exactly that - Kryan is simply you typical arcadey-consoley boss creature of this variety:
Edit: ok bros, skip to 8m 55s - Codex cannot into embeded timers.
You use exactly the same mechanics durring that fight and the battle with Kayran - dodge the attacks, hit the weak spot with ability, deal damage while the creature is dazed, rince and repeat. Hell, in this video it's even more complex, because the enemy has varied forms of attacks and it's never just 'dodge left || dodge right'. And yes - this boss battle takes place not far from the beginning.
In other words - fucking platformers have more complex and tactically challenging boss fights than TW2.
And it's so painfully obvious that gameplaywise boss battles are so untactical, so lackluster, so boring, and so cheap that I can't wrap my head around how this could appear in alleged "hardcore story-driven RPG".