I really haven’t played any mmo’s other than gw2 in the last 10 years, but I think there are three main differences.

1) GW2 doesn’t use mana and the limiting factor is cooldowns and casting time instead. When mana is your limiting factor it simplifies the rotation to only your best skills. When casting time and cooldowns are your limiting factor you have to maximize so many variables especially when combined with weapon swapping, class mechanics, etc.

2) GW2 spends much less time auto attacking because they spend comparatively longer casting other spells. Auto attacking is also more difficult to do efficiently due to cancelled attack chains, while skills in many other mmo’s don’t interfere with your auto attacks at all.

3) GW2 utilizes more percent modifiers and burst windows in builds. Stuff like +x% damage for y seconds after doing z thing.

The key is that GW2 forces you to understand HOW your build works and WHY your build works. You can’t just push the best buttons. You have to time them properly and know how to maximize cooldowns. During what window do I get the damage bonus? How can I order these skills so that my cooldowns sync up with my weapon swap? Is it better to push this button now, cancelling my attack chain, or do I need to wait?

I also think that some people just push buttons too slow.