If you just like watching webseries with Felicia Day in them, you're in luck, as there are a couple of options. Before Dr. Horrible, she wrote and starred in her own webseries, The Guild, a light comedy about a bunch of World of Warcraft players who are one day drawn away from their computers and brought together in an unprecedented meeting in the real world. A little bit Penny and a little bit Liz Lemon, Day's "Codex" is just a sweet gamer girl trying to make it in a cold and lonely and sometimes pretty strange world.
There's also The Legend of Neil, a webseries written by Sandeep Parikh ("Zaboo" from The Guild) and also featuring Felicia Day. It's a about a guy who gets sucked into a Zelda game one day by improbable means, and the humor, while generally fairly crude, is also pretty irresistible. I'm sure that many hours logged in front of a console playing Zelda will also enhance the viewing experience significantly.
Goodnight Burbank, which somewhat grandiosely claims to be the "World's First Character-Driven Comedy Created for the Internet", and further describes itself as "a little 'The Office,' a little 'The Daily Show'" (to which I would probably add "a little 'Sports Night'", a comparison inevitably evoked by the setting), is a fictional nightly newscast in which the anchors let their hair down to gripe and jibe in-between news segments with headlines ripped from real current events. Some of the humor is a bit broad and rather stock, for instance the stereotypically geeky middle-aged newscaster who lives with his mom, remains a virgin, and talks incessantly about Doctor Who and his fantasies involving Klingons, or the episode which is entirely given over to a by-the-numbers retread of an old Abbott and Costello gag (yeah, that one), but the energy and earnestness of the production make it easier to forgive the occasional creative shortcut and just enjoy the simple laughs.
Honesty is a comedy with the simple premise that, when placed in a variety of typical social situations, everyone always says what they're really thinking. This clever, funny series won the 2007 Webby for long form or series comedy.
Wainy Days is billed as the "fictionalized life" of David Wain, which is probably stretching it a bit. Drawing on Wain's sketch comedy roots, the short episodes of the series are absurdist in tone and sometimes dive off the deep end into the simply surreal. Superficially, they're about Wain's romantic misadventures in an outrageous New York City, where people will apparently say and do the darndest things. The series is on its third season and is the winner of the 2008 Webby for long form or series comedy.
Best for last: Horrible People, created by A.D. Miles, is unexpectedly perfect. It's a fake soap opera that takes place during a momentous and very eventful engagement party in which the intrigue and the bodies just keep piling up. The over-the-top plot twists are played straight with a soap's overstated sense of drama, and the tone of the humor, about broken family dynamics and rich people behaving badly, repeatedly put me in mind of Arrested Development. It could be just that the heartless, scheming Mother and Lucille Bluth are drawing from the same archetypal well, or that callous, self-absorbed Michael seemed at times to be channeling Gob (who for his part already behaved like he was living in a bad soap opera), but I could almost hear the ukuleles in the distance.
Creatively, Horrible People belongs to the same The State/Wet Hot American Summer/The Ten talent pool that spawned Wainy Days, and even features a brief walk-on by Wain, but Horrible People benefits from the more structured plot and focused thematic directive of its fake soap format, and presents a more cohesive and rewarding experience than its free-associative, adolescent comedy brethren. The internet is great for fostering that kind of no-rules absurdist comedy, essentially professional versions of kids messing around on YouTube, but Horrible People proves that content produced for the web can be much more, well, televisual.
A golden age of web video seems to be dawning. Having "Horrible" in the title seems somehow auspicious, but I'm hopeful for new projects that can combine the best of uncensored creative freedom and seasoned professional expertise to create exciting shows that comb new territory and tell new stories, without necessarily resorting to college-boy humor and webcam hijinx. If you want to discover more quality work, the annual Webby Awards are a good place to start. Oh, and if you still haven't seen Dr. Horrible, it's still up on Hulu, so I guess that whole "limited time only!" thing was a psych. Off you go.