We all have different perspectives as to what it means to beat an expansion; some people think you have to kill the hardest boss on hard mode in 25 man. For others, it's to finish all the meta-quest achievements in the expansions' zones. I've seen people tell me they were satisfied when they had killed the last boss, no matter what the degree of difficulty (i.e. 10man normal).
But I'm interested in what YOU think might just be the moment to personally call an expansion beaten.
Thoughts! Go!