I seriously underestimated Joss' guts when it comes to story-telling. I saw the darkness looming in the story, but I didn't think he could go all the way into Wagnerian tragedy with a premise as silly as "Dr. Horrible." And yet he did . . . and convincingly, too.
I should have known there would be blood. Bad Horse had called for blood repeatedly. It couldn't have been otherwise. And death was really too good for Captain Hammer â€“ he needed to be utterly humiliated for the story arc to complete itself. So the blood had to be Penny's. And Billy's descent into full-bore villainy is seen for the human tragedy it is. Billy's decency never left him â€“ in spite of his rage, he hesitated to pull the trigger on Captain Hammer, even while calling for "no mercy." Horrible's "victory" was achieved, ironically, by his own incompetence at evil â€“ had the freeze ray held a minute longer, or the death ray not blown up in Hammer's hands, things would have turned out very differently. And equally telling that it's Hammer's arrogance (and genuine lack of remorse) that ultimately defeats himself and does in Penny, too. So Horrible stumbles across the threshold into full-bore villainy, more the victim of a corrupt society than a willing agent . . . and we feel, with him, the hollowness of his victory, and ultimately, the complete loss of any feeling at all.
"Feeling" is the real theme of the entire story. Both Billy and Penny show their humanity in their capacity to feel pain, which opens to them the capacity for empathy and connection to other people. Captain Hammer evidently never felt a moment's pain in his whole life . . . making him an arrogant self-serving tool. When Hammer does finally feel pain, his capacity to oppress is completely undone. And only when Billy's capacity to feel is extinguished, numb with grief and horror, can he become truly Horrible.
"Pretending" could contend as the central theme, too. Joss mercilessly pounds on the shallowness and banality of society in the final episode, demonstrating how it hides from inconvenient truths with pasteboard heroes, thin veneers of caring over the power of the status quo. I thought it was a sweet to see Penny sitting in the Coin Wash, obviously waiting for Billy, extra frozen yogurt at the ready, and she asks herself, "Should I stop pretending?" Even at that point she knew she was playing along with something less than genuine, denying her real feelings for Billy in favor of the security of being with the established power of Captain Hammer. She alone had the sense to be mortified by Captain Hammer's speech at the dedication . . . but too late. All that pretending â€“ Hammer pretending to be compassionate, Penny pretending to love him, Billy pretending to be the villain he really wasn't â€“ was what ultimately creates the tragedy.
I love the last cut of the film. We see Dr. Horrible fully realized, his white coat and gloves traded for red and black, walking into his place in the Evil League of Evil . . . but at the very last we cut back to Billy's blog. Billy: still human, still small and alone, calling out to the world from his blog, still a human being. This is "Horrible"'s greatest achievement: to humanize evil, to see the person behind the mask.