Live TV episodes became something of a gimmick a few years ago, when "ER" and "The Drew Carey Show" dabbled in them, after the Fox sitcom "Roc" went live on an extended basis.

Still, it's been awhile, and the live "30 Rock" that aired Thursday (this review's obviously based on the West Coast version, but they did the same for the Eastern time zone) underscored how the sizzle associated with the idea is often superior to the execution.

The best bit came early and was used several times — having Julia Louis-Dreyfus stand in for Tina Fey when Fey's character, Liz Lemon, would flash back to earlier events, as she regularly does during the series. Asked why her doppleganger was hotter, Lemon attributed it to "'Seinfeld' money." Clever stuff.

After that, though, the episode essentially played like a mediocre collection of "Saturday Night Live" sketches, complete with several "SNL" alums popping in, bogus commercials and drive-by appearances from high-profile guest stars Matt Damon and Jon Hamm. The episode was also partly scuttled by a gag that was intended not to be funny: Having Tracy Morgan's character become enamored with breaking character and cracking up. Each time they went to that bit, it essentially brought everything to a grinding halt. It was almost enough to make you start seeking laughs over at MSNBC, where they were running lowlights from the Harry Reid-Sharron Angle debate in Nevada.

Having lost its post-"The Office" lead-in, "30 Rock" is drifting through a satisfactory year in its new, earlier timeslot. Of course, the best thing that happened to "30 Rock" was probably CBS' "$#*! My Dad Says," whose mediocrity is an invitation to "The Big Bang Theory" viewers to conduct experiments with the remote control.

Give the NBC show credit for trying something different at this stage of the game, but by almost every measure — from buzz to ratings — its best days are almost surely behind it. In fact, to put it in show-within-a-show terms, "30 Rock" — so inventive in poking fun at its network and corporate parent during the down days under GE's ownership — finds itself fading just as Kabletown prepares to take over.

Update: For NBC (and "30 Rock"), mission accomplished: The stunt produced a spike in ratings, and brought the show within a hair of matching "$#*!" in key demos.

From NBC's release:

"30 Rock" scored season highs in 18-49 and total viewers and matched its highest 18-49 rating since December 10, 2009, when it still aired in the 9:30 slot. In total viewers, this is the biggest audience for "30 Rock" since March 18, also in the 9:30 half-hour. Week to week, "30 Rock" is up 43 percent in 18-49 rating (3.0 vs. 2.1) and 36 percent or 1.8 million persons in total viewers (6.671 million vs. 4.899 million). Last night's "30 Rock" finished within a tenth of a rating point of the time-period lead in adults 18-49 and won the slot in adults, men and women 18-34 and men 18-49.

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