There has been a list created by several WOW gamers that show how many elements of the game, (Raid Boss encounter wise), are in fact based on luck and randomness, as opposed to skill. Take a look at the list and judge for yourself!

-Vaelstrasz and his burning adrenaline.
-Chromie and his breaths (not as extreme, but still annoying to get time lapse and corrosive acid, especially with time lapse still bugged > -Skeram and whether all 3 port to the same platform, MC all the tanks over there and decide to spam the healers with earth shock.
-Fankris and whether or not all 3 bugs come at the same time.
-Sartura and whether they go after just healers or not (well their stunable most of the time, and it is "controlable" so it's around the same as chromie)
-Yauj and whether she heals or not (same deal, interruptable, but can still !&$% you over)