'Pan Am' and other shows that fly

The biggest show on Earth is about to commence, with major reboots of returning series and 27 new network series, including a shiny newcomer that looks an awful lot like TV's most popular reality series. (Yes, every fall has its X factors, but this one actually has "The X Factor.") TV fall seasons are, of course, about profligacy, and as always, much will come, and much will also go. Here are four key trends that may influence your picks in that inevitable winnowing process:

The cast reboot

Blame coincidence along with a certain star's predilection for "goddesses," illegal substances and blistering diatribes against employers, but three venerable hits will get new leads this fall. Ashton Kutcher joins "Two and a Half Men" just as dirt is thrown on the coffin of dearly departed Charlie Harper (Charlie Sheen). James Spader plays Dunder Mifflin's new CEO, Robert California, on "The Office" as a boss with unsettling management style. Speaking of which, the replacement for Michael Scott (Steve Carell) should be named this fall, too. Meanwhile, Ted Danson joins "CSI" as D.B. Russell, a family man with a hippie mien who doesn't (presumably) quail at the sight of blood.

Why you should watch Both Spader and Danson are superstars of the small screen who will add life to declining franchises, while CBS' triage on "Men" is a rare spectacle indeed. Everyone will have an opinion on this reboot.

The high concept gets higher 

Years ago, TV needed a name for kooky program ideas that didn't conveniently fit into any genre, so this neither-fish-nor-fowl concept was cheerfully christened "high concept." High concept can be fertile soil (from "Knight Rider" to "Lost") or barren. This season brings "Terra Nova," about a family blasted 85 million years into the past; "Unforgettable," about a woman who forgets nothing; "A Gifted Man," about a surgeon who has visitations from his dead wife; "Person of Interest," about crime stoppers who stop crimes before they happen; "Grimm," about a detective descended from a line of supernatural hunters; and "Once Upon a Time," about fairy-tale characters living in a contemporary town.

Why you should watch High concept usually means special effects, and some of these newbies boast some budget-busting flourishes, most notably "Terra Nova," which promises a dinosaur (or more) per week. But the high-concept drama with the most breakout potential -- and expected to land on most critics' top 10 lists -- should be light on CGI: "Person of Interest."

Nostalgia mini-binge

Every season seems to have a remake of a once-popular series, so ABC newcomer "Charlie's Angels" doesn't qualify as nostalgia as much as cagey opportunism. But a pair of '60s-era dramas certainly do -- "The Playboy Club" will re-create the early go-go years of Hugh Hefner's Chicago club, while "Pan Am" celebrates stewardesses (and their pillbox hats).

Why you should watch Costumes and set design alone make these fun diversions on the fall landscape. "Pan Am" is widely considered one of the best new shows of the fall.

'The X Factor' factor

"X" doesn't so much represent a trend as it does the culmination of one. But with "American Idol" and "The Voice" returning in winter, it's worth wondering when enough is enough.

Why you should watch Simon Cowell and Paula Abdul, naturally; plus Cowell has absolutely, positively promised a superstar. Expect another water-cooler series -- at least in the early weeks.