Normally, something with that title would sound like the kind of overly precious, indie-pandering project that I run screaming from. This one's got a major plus on its side though, and his name is Joss Whedon.
Whedon is the mastermind of the television series Buffy the Vampire Slayer, Angel, Firefly and its movie Serenity, and Dollhouse. I've never watched much Buffy or Angel, but Dollhouse and especially Firefly are fantastic, balancing humor with serious drama and very real (and dangerous) stakes for the characters. A great quote I picked up about him from somewhere: "Joss Whedon's genius is that he can have you fall down laughing until the moment he decides there will be no more laughter." I think that describes his style perfectly. I will have reviews of both Dollhouse and Firefly here at some point, but in the meantime take this as my recommendation that you watch them.
Dr. Horrible's Sing-Along Blog is like a condensed version of all of Whedon's sensibilities and strengths. It's incredibly silly, but still manages to evoke strong emotions by the time it's over. The story revolves around Dr. Horrible (Neil Patrick Harris, continuing to show off his comic chops), an aspiring evil-doer who is trying to gain entry to the Evil League of Evil, a sort of criminal mastermind social club headed by the nefarious Bad Horse. The bad Doctor, however, finds himself falling for Penny (Felicia Day), the cute redhead at the local laundromat, and constantly being thwarted by his smug arch-nemesis (the always welcome Nathan Fillion), Captain Hammer. Oh, and the 'sing-along' part is not just part of a catchy title; this is basically a musical, and the songs are hilarious and well-done, with both Day and Harris shining in their singing parts. All of this in just over forty minutes, too.
This was done as fun little project during the writers strike of last year, and it's basically a family affair, with Whedon's brothers and sister-in-law as the other writers. That doesn't mean they half-assed it, though, as the DVD includes a making-of documentary and possibly the best special feature ever: Commentary, The Musical. If you like to laugh and enjoy silliness, this is for you. I don't know if Netflix carries it, but you can purchase it at Amazon or Barnes and Noble for reasonable prices.