First off: Dr. Horrible = Barney Stinson (NPH's character on How I Met Your Mother). So much of the actual text felt shout-out ("BTW," "tell your friends," blog, bonus: moist, volunteering at the soup kitchen), but it was more than that.
The first two acts were enjoyable. The musical numbers were very evocative of OMWF. (Every time the Bad Horse chorus popped up, I thought, "My master has the Slayer's sister hostage at the Bronze.")
I literally laughed out lout at, "The hammer is my penis."
Given the sense I'd gotten from reaction posts, I was expecting an unhappy ending come Part III and my guess was that Dr. Horrible would accidentally kill Penny.
I appreciated that Penny realized Captain Hammer's sleaziness, but why is her last line, "It's okay, Billy. Captain Hammer will save us"? Out of everything, that's what really bothered me.
I laughed out loud at Captain Hammer's "Someone maternal!" line but thought at the moment that he was actually physically wounded. I didn't realize anything had happened to Penny until we literally saw it. And I think I didn't really realize that was what Captain Hammer was so pained about until we saw him on the therapist's couch (which I didn't entirely know what to make of, since we know he doesn't really care about her as a person -- is it just that he's never lost anything he wanted before?).
It's an interesting critique -- that Dr. Horrible finally gets recognition as a Big Bad Evil because he killed Our Hero's girlfriend, whose name the newscasters mostly don't even know (or care about), but I feel like that critique is too brief to really be noticed and that on the whole it's just a very unsatisfying ending. I am really intrigued by the last moment of the film when the video feed cuts to just Billy (not Dr. Horrible) on camera -- as if this had all been a fantasy sequence or something.
Heh, the newscasters were David Fury and Marti Noxon. And the Evil League of Evil included Doug Petrie ("Professor Normal") and Drew Goddard ("Fake Thomas Jefferson"). And Jed Whedon was "Dead Bowie" (and Bad Horse Chorus #2). And Ben Edlund gets first billing in the "With a very special thanks to..."
And of course Penny was played by Felicia Day, who played Vi (one of the S7 Potentials) on BtVS.