Neil Patrick Harris in Dr. Horrible's Sing-Along screen grab courtesy Mutant Enemy Productions
Two of my favorite things in all of show business- musical comedy and Joss Whedon - combine in the funniest, freshest TV special of the summer, which happens to be available only on your computer starting in mid-July.

I had the great good fortune late last week to get a sneak peek at all 42 minutes of Dr. Horrible's Sing-Along Blog, Whedon's stylishly scrappy, lovably cheesy and insanely tuneful return to the form for which he showed such incredible aptitude in the classic "Once More, With Feeling" episode of Buffy the Vampire Slayer.

Dr. Horrible, written during the writers' strike and filmed in six days this spring "on favors and waivers" by a crew of longtime Whedon loyalists, will be streamed for free in what Whedon cheerfully calls an "Internet miniseries event" on the show's official website ( www.drhorrible.com) in three chapters. Part 1 will be available Tuesday, July 15, with the following segments (each roughly 14 minutes) available July 17 and 19. All three parts will stay up only through July 20, but deals are currently underway to make it available for downloading shortly thereafter.

The ultimate goal: a DVD, at which time perhaps enough profit can be made "to pay the people who were doing us favors," says Whedon. In a chat following my nearly private screening (attended only by Whedon, a few of his New York-based agents and me), Whedon confided, "We're already working on some of the DVD extras, which are going to be the finest in all the land. We're actually going to do, in addition to the commentary, what we refer to as 'commentary with an exclamation point'! A musical commentary that is a completely original musical, that is all commentary songs, and we're writing that now." As I gasped at that audacious notion, he continued: "We're just piling it on. We're like, we're going to make more fun of the idea of extras than anything else."

All in keeping with the sweetly satirical tone of Dr. Horrible itself, which reminded me at various times of Little Shop of Horrors and, in its more bombastic moments, Sweeney Todd (a Whedon favorite, and mine as well).

[Some mild spoilers follow.] In the title role, and starring with adorable panache: How I Met Your Mother's Neil Patrick Harris, whose musical-theater chops Whedon discovered when attending the 2004 Broadway revival of his idol Stephen Sondheim's Assassins. First seen perfecting his cackling laugh in hopes of being taken seriously by the Evil League of Evil, and reading snarky e-mails from his skeptical online following, Harris plays a wannabe mad scientist - "The world's a mess, and I just need to rule it" - who's perfecting a "freeze ray" with which he can stop time and, according to one lyric, "stop the pain."

Because, you see, Dr. Horrible - real name "Billy" - does have a heart, and it belongs to winsome do-gooder and Laundromat buddy Penny ( Felicia Day, one of the "potential" slayers in Buffy's final season). Some of Harris's best work, when he isn't singing arias of evil and comically mugging, is in his bashful, stammering pining for Penny - who naturally falls for Dr. Horrible's arch-nemesis Captain Hammer, a buffoonish cad of a narcissistic superhero ("I don't go to the gym. I'm just naturally like this") played with hilariously villainous cartoon relish by Firefly vet Nathan Fillion.

Everyone in this tortured triangle gets big numbers, from lyrical ballads to soaring (and usually very funny) anthems. Quite a lot of music, written by Whedon with his brother Jed, is crammed into this mini-movie, and if you're like me, you'll want to hear it again and again.

So how did we get lucky enough to get a new Whedon musical at this point in time? Let's just say it's one of the few positive things to come out of the writers' strike.

"I was really sick of not doing things. I'd been writing movies nobody was making. I got tired of that. And even though I had this series (Fox's Dollhouse) coming up, we were on strike- and well, I thought we were going to hold out a little bit longer- but it just felt right," Whedon says. Looking back on the Buffy musical episode, he says: "I never wanted to leave that musical place. I thought about doing this as a podcast just so I could write songs, like a radio show. And then when the strike happened, everything was about making online content. But everything was very overblown. Or underblown. It was either me and my video camera in my backyard or let's partner up and get millions of dollars. Neither of these things was gonna fit the paradigm that will make me a musical, so I finally decided to do it myself."

The idea, he says, "was to show that you can do this [original Internet content] on a very different scale than people are thinking about. I felt like we stretched our dollars just as far as they will go. It's a pretty extraordinary piece even at the price tag it would cost to normally produce it if you couldn't call in any favors." (He won't go on record to discuss the budget, which was much less than the usual hour of TV production, but jokes that it cost "twice as much as Once.")

"Also, we were able to just completely bypass the system- not in a sense of giving the finger to the majors, because we'll probably end up partnering for distribution with somebody if they're interested- and some of the reason this came out the way it did was because people who are employed by the big guys could afford to do this. And we got the Universal backlot for a song because of our relationships there, and people were very sweet. I mean, during the strike there was a certain amount of justifiable bile, but my relationships with the people who actually produce the things, I like to think of as very strong."

Many relationships, personal and professional, came into play in making Dr. Horrible. His brothers Jed and Zack helped him write it, along with Jed's fiance Maurissa Tancharoen. Jed appears as part of a recurring Evil League of Evil chorus and Tancharoen can be seen as one of Captain Hammer's fawning groupies. Whedon cohorts Marti Noxon and David Fury, who both did cameos in "Once More With Feeling," return as snarky newscasters. And then of course there's Fillion, a part of Whedon's repertory company since Buffy and Firefly. "I'd heard him sing, but I just knew that even if he couldn't, he could sell it. He's Nathan, and he was great."

As for casting Neil Patrick Harris, all it took was a phone call. "We all agreed there was really nobody else that should play Dr. Horrible. I didn't even get the sentence out before he said yes. And then I sort of got defensive (Whedon lapses into fanboy-speak): 'No no no, it's really going to be good,' and Neil's like, 'I said yes.' And I said, 'No no no, I mean, but I mean the point is, is mean I mean' I couldn't handle it."

The strike ended before filming started, so they postponed the shoot until a break in How I Met Your Mother production in March (wrapping around the same time as the Paley Fest's Buffy reunion which I moderated).

How did this affect Whedon's work on the Dollhouse pilot? "I told Fox going in that I'm making this, it's going to take six days of shooting, and during those six days you'll get bupkis. They're like it doesn't matter, you're still filming your pilot- that you haven't broken yet- in two months." He sighs. "It's been quite a time."

Which begs the question: Could there ever be a musical Dollhouse episode? "Well, Eliza (Dushku) has a lovely voice. But first I have to make a normal Dollhouse, which is hard enough." So how's it going? "There's still tweaks. Birth pangs. It's never simple, but it's going well."

As for Whedon's Internet future, while there has already been talk of Dr. Horrible sequels, for now Whedon is waiting to see how this experiment plays out. "Whether this has any impact on the Internet is unclear to me. It will be something that hasn't been done. And although some people came up with a plan on how to monetize this right away, our first priority was to put this out. We do it for the fans, we do it as an advertisement for itself and for just this culture, this idea of people who are doing something smaller scale but hopefully in such a way they can reach a lot of people. And maybe then it can make us an eleven-ty kadillion dollars. Or maybe it won't."

If there's any justice, Dr. Horrible will eventually make a bundle. Far from horrible, it's terrific.