Maybe I'm a lil late on the bandwagon, seeing as the series is no longer available for free on the official site, but it's still available on iTunes if you live in the US or Canada, and it shall at some point be available both in audio (soundtrack) and video (DVD, complete with a commentary track that is itself an actual song - !!) form.
You probably don't need to read another glowing review, admiring the typically-Joss-Whedon-esque, brilliantly witty dialogue (highlight: "Gosh, look at my wrist, I need to be going", says a watch-less Neil Patrick Harris at the news of Nathan Fillion's arrival), the charming cast (the aforementioned pair, as well as Felicia Day, a Buffy veteran), the supporting characters (Bad Horse, Moist - the latter a not-so-super-villain, whose power is to make things damp; the former is kinda self-explanatory)... ah well.
Instead (as well?) here's a lovely song for you to be happy to. Listening to the new Ben Folds material actually kinda made me think of these songs - piano-based, amusing, that's pretty much where the similarities end, but still. They're also both brilliant. So, y'know, yay:
mp3: Neil Patrick Harris & Felicia Day - Cannot Believe My Eyes
(from Dr. Horrible's Sing-Along Blog, soundtrack coming soon-ish)