What do you think is the most important thing in a boss encounter?
For me it has to be the mechanics of the battle.
Preferably fun mechanics like Malygos stage 2 where you ride disks to kill the mages in the air. Or even the lootship battle even though it was easy, it was fun rocketing to the other ship killing the mage, rocketing back and using the cannons.
And Gutblock in DM for cata. Even though I wiped on it millions of times his 2nd stage is still fun, having to avoid the firewall and still DPS him.