1) He froze several allies which you could break the ice to free them
2) It was shooting flaming balls which did substantial damage if you didn't dodge
3) He spawned allies
4) He flew into the air so he was out of melee reach
Yeah, this is totally *like* a rancor. Somebody hand a nobel prize to jam for pointing the obvious. Everything is a rancor.
Difficulty can be adjusted, but let's face it: (1) however epic the fight is, it's not fun if you're getting owned, it has to be challenging but not frustrating, (2) the rancor in question didn't look hard either, and even if he was tough, it was all stats no actual play skill... as in, can you out-dps him.
Conclusion: GW2 is the place to go for epic boss fights in the MMO genre.