It was very Spartacusy: especially the "Will we betray each other in the arena, or team up against our common enemy?" plot point. Also, I got a papercut from one of the character sheets, and there was a bullet-time fountain of CGI blood.
I was surprised that the Defiler feature only hurt allies, not everyone. I guess it makes you more of a jerk for using it, and jerkiness is one of the only markers in D&D separating the "good" murderous lunatics from the "evil" murderous lunatics. That and necrotic vs. radiant damage.
Also the Defiler feature is only usable on dailies, not on every attack as I originally thought. This makes it less open to abuse, but also a little less interesting. I think they could have gone bigger, since it was the force that ended the world.
I really liked the "risk breaking your weapon on a natural 1" option. It's fun that something tactically interesting happens on a 1. I do wonder how it will work at higher levels, when PCs have magic items to risk. Would you risk breaking a +3 sword (resale value 1800GP) to reroll an attack in a level-11 encounter (expected loot from the whole encounter about 1800GP)?