...it would look a lot like Doctor Octoroc's brilliant re-imagining of the web series. I'm not sure why anyone would go to the lengths of creating something like this, but the world is better for it.
Admittedly I was a little bummed when I found out that it's strictly a video and isn't interactive, but I guess creating an entire game would've been even more insane and time consuming, so I'm not about to complain.
If you're new to the Dr. Horrible phenomenon, it was a web series starring Neil Patrick Harris, Nathan Fillion and Felicia Day. Written, directed and produced by Joss Whedon of "Buffy" fame, the 3-episode series is a staple of nerd culture and should be watched by all. It's no longer available for free streaming, but you can find it on Amazon or iTunes, if you don't mind a price tag with your entertainment.