I was blown away by the Doctor Horrible web series that debuted in 2008. My whole family loves it. We sing the soundtrack (Dr. Horrible's Sing-Along Blog)all the time. My wife picked up the Dr. Horrible graphic novel for me for Christmas, knowing that I love comics and anything by the Whedons. My major complaints are that it wasn't long enough and there is no accompanying soundtrack!
The stories were penned by Zach Whedon and focus on the major characters, as expected. Each one is an origins story, for lack of a better term and really gives a lot of insight into the characters. There several telling panels where you see the delusions that Doctor Horrible and Captain hammer actually suffer through. Penny's tale was particularly satisfying because you get a glimpse of what might have happened if Doctor Horrible had just been himself.
This is a great read and adds to the Dr. Horrible universe. The graphic novel had me jonesin' for more!