In a room full of tall players
I was in a room in the Imperial Sewers full of elven folks (including High Elves) chilling with the drink animation (one of the only few ways to take off the helmet). The fact that the room is full of tall people and my character is towering over everyone else is something that is mainly unique about this polymorph. The size isn't just the only thing, though. Here are others.
Not taken from something already in-game (Umaril is not in ESO)
Special effect flaming eyes
I only wish that the helmet was removable.