Make it so that not all the boss fights are stationary and players have to move around to avoid taking damage from various factors: Boss special attack, environmental changes, etc.
Also... This sounds like you just took Aspidochelone and gave it a WoW spin. I approve though.
I think you nailed one point right on the head, and WoW has been leaning towards what I am essentially suggesting. Stationary boss fights that last a very long time are the WORST battles.

Movement, using the environment, and scripting ( something WoW uses ) to add depth to the fights is a step foward. FFXIV has these capabilities. We've seen in leves where monsters run, Moles that burrow underground, and, as mentioned before, gnats that dissapear and reappear.

Aspid was a boring fight though lol. He is a giant turtle sure, but... not necessarily the most interesting encounter around.