LOS ANGELES - Jay Leno's new prime-time experiment on the struggling NBC network pulled in big audiences, according to early ratings figures on Tuesday, but mostly underwhelmed TV critics.

Some 17.7 million Americans tuned in for the closely watched debut of The Jay Leno Show at 10 p.m. on Monday, preliminary numbers from Nielsen Media showed.

That compares to the roughly 5 million strong audience that used to regularly watch Leno's old Tonight Show and puts the new chat show's first outing on a par with crowd pleasers like the CSI crime franchise on rival CBS.

Leno's move from his comfortable late-night home to the nightly prime-time slot traditionally occupied by expensive scripted dramas on leading U.S. networks is being scrutinized by the network TV industry as it struggles to cut costs and retain audiences.

General Electric Co's NBC network has been particularly hard hit and has been struggling in last place for four years among the leading four networks.

But the debut of the new show, which featured appearances by comedian Jerry Seinfeld, rapper Kanye West and comedy skits involving talk-show host Oprah Winfrey and President Barack Obama, left critics mostly unimpressed with many saying it seemed tired and old.

Sixteen minutes into the new The Jay Leno Show, it was difficult not to panic. This is the future of television? This wasn't even a good rendition of television past, wrote Los Angeles TV critic Mary McNamara, adding she hoped the hour-long show will get better, much better.

The Hollywood Reporter said the menu seemed familiar for a new show where the stakes were so high for NBC.

Five nights a week of 'Jay Leno' presents a too-high risk factor to deviate too far from the norm -- and what's left is an unsettled sense that they're throwing things on the wall to see what sticks, wrote Randee Dawn of The Hollywood Reporter.

(Reporting by Jill Serjeant; Editing by Eric Beech)