I know what you mean.
WoW was fun when I first started playing and didn't know what I was doing.
Wants I learned how to play well enough it got boring.
"Good" players have a rotation of attacks that they do over and over again, its very repetitive and boring. It's also very unrewarding, unlike singleplayer games where when you do a quest it actually changes things instead of nothing happening except for an exp gain.