HBO shocked industry insiders on Tuesday when it canceled three series in one fell swoop. Hung, Bored to Death, and How to Make it in America all got scrapped after three, three, and two seasons, respectively. At the same time, Enlightened, the little-seen dramedy starring Laura Dern, was renewed for a second season. Why was the trio of shows canceled while Enlightened got a pick-up? Here, a brief guide:

What are these shows about?
HBO's "unprecedented decision" ends several cult-favorite shows, says Sean O'Neal at The A.V. Club. First is Hung, a half-hour comedy starring Thomas Jane as a teacher who moonlights as a male prostitute. Bored to Death was a genre-bending hipster-noir-comedy starring Jason Schwartzman, Ted Danson, and Zach Galifianakis. And How to Make it in America followed a group of ambitious twenty-somethings living in New York City. Spared was Enlightened, starring Dern as a career woman undergoing a spiritual awakening.

Why were the shows canceled?
Ratings had a lot to do with it. Hung, Bored to Death, and How to Make it in America's ratings were higher than Enlightened's, but they've been sharply falling over the past year, says Lacey Rose and Lesley Goldberg at The Hollywood Reporter. Hung's 930,000 viewers for its season three finale are a far cry from the 2.31 million who tuned in for the end of season two. Bored to Death dropped from 1.1 million to just 240,000 viewers in the span of a year, and How to Make it in America bottomed out with just 560,000 viewers.

Were these shows any good?
The trio "fell far short of garnering the kind of accolades" that Boardwalk Empire and Game of Thrones won. "As evidenced by the smaller audiences programs like Mad Men and Breaking Bad garner," says Kevin Yeoman at Screen Rant, "accolades and awards typically mean a great deal when it comes to the longevity of a series." Enlightened, which mustered just 200,000 viewers for its season finale, still managed to pick up two high-profile Golden Globe nominations, for Best Comedy and Best Actress in a Comedy, and has been popping up on numerous critics' year-end Top 10 lists. 

Are there new shows in the pipeline?
There sure are, and it seems like HBO is trying to make room for them. Among the shows slated to premiere in 2012: The Ricky Gervais comedy Life Is Short; the Julia Louis-Dreyfus political comedy Veep; Girls, from indie darling Lena Dunham and Judd Apatow; 40, a new series from Entourage creator Doug Elin; and a new show from Sex and the City creator Darren Starr called Viagra Diaries, starring Goldie Hawn. That's not to mention the hotly anticipated new drama about a cable newsroom written by Aaron Sorkin (The West Wing, The Social Network).

Are critics miffed?
Somewhat. Bored to Death's cancellation is the "most upsetting," says Michael Arbeiter at Hollywood. The "magnificent comedy" was just finding its groove, and boasted an indelible performance from Danson each week. Worse, says O'Neal, the abrupt end leaves several cliffhangers unanswered. Still, says Ken Tucker at Entertainment Weekly, the decision to keep Enlightened signals a refreshing shift in HBO's priorities. The "beautifully acted" show more than deserves a second season, and adheres to the industry trend that women — as exhibited by Parks and Recreation, Up All Night, Happy Endings, and New Girl —  "are making some of the most vital comedy moves right now."

Sources: A.V. Club, Entertainment Weekly, Hollywood, Hollywood Reporter, Screen Rant