Los Angeles - Showtime has arrived at a delicate point in its history, changing executives, pushing deeper into scripted-series territory, scoring 23 Emmy nominations in 2010 and leaving its image as an also-ran behind.

Thankfully for discerning viewers, Showtime is serious about serious acting.

And now comes "a new chapter," the network promises. Expect it to hold more dark, intense dramas with respected performers exploring the depths.

Outgoing programming boss Robert Greenblatt steered the network to "one of the most successful lineups in all of television," according to Matt Blank, chairman of Showtime Networks. Showtime this year was the only premium TV provider to grow in subscribers; the network is now in 18 million homes.

Greenblatt recently surprised the industry by leaving at a peak, reportedly seeking bigger challenges. The incoming chief, David Nevins, whose credits include "Friday Night Lights," starts Monday.

Showtime is poised as one of three networks - with corporate cousins CBS and CW - serving up different styles of shows with different types of stars, aiming at specific audiences. Each of these Viacom properties targets a specific archetype; those types are only becoming more distinctive.

CBS is full of male buddies, cop heroes, lawyer protagonists, men's men. Think Simon Baker, David Caruso, and, this season, Jim Belushi and Tom Selleck.

CW is full of adolescents with barely formed libidos. Think "Gossip Girl" and, coming up, "Hellcats," about a high-school cheerleading squad.

And Showtime is the place for smart actors in some wildly twisted stories: Mary Louise Parker in "Weeds," Edie Falco in "Nurse Jackie," Michael C. Hall in "Dexter" and Toni Colette in "The United States of Tara."

Insiders are guessing Greenblatt will end up at a broadcast network, maybe the revamped Comcast-NBC.

What Greenblatt did for Showtime was to make the also-ran network a real player in the scripted original series game. His main achievement, the Hollywood Reporter declared, was "remaking the network's No. 2 status from the also-ran you pity to the underdog. Think Avis-Hertz."

He did that by employing serious, accomplished actors, strong writers and playful use of established formulas.

He pushed antiheroes, if not outright sociopaths. A drug-dealing mom; a pill popping and adulterous nurse; a multiple-personality-disordered wife and mother.

And this fall, a sly, subversive cancer patient joins the lineup. Laura Linney, whose character on "The Big C" has stage-4 melanoma, told critics she and her co-producer have considered doing a crossover episode with "Weeds" that takes medical marijuana as its theme.

Upcoming casting news: Richard Dreyfuss and Linda Hamilton join "Weeds." Peter Weller has a stint on "Dexter." David Duchovny and "Californication" return in January.

Showtime has picked up 10 episodes of Lisa Kudrow's "Web Therapy."

Cynthia Nixon, Liam Neeson and Idris Elba will have guest roles on "Big C."

John Wells is producing the "unapologetic" series "Shameless," due in January, starring William H. Macy.

Post-"Tudors," the network is moving on in spring 2011 to cardinals and popes: "The Borgias" with Jeremy Irons, done as the original Italian crime family.

It remains to be seen how Nevins will change or extend the current trajectory. If it ain't broke ...