( CNN ) -- You 'd think someone who lasted 17 years as host of a television program in this day and age -- particularly a show as venerable as NBC 's `` Tonight Show '' -- would be receiving praise and honor . Jay Leno has rarely impressed critics , but he 's been the No . 1 late-night host for almost 15 years . Not so Jay Leno , whose final `` Tonight Show '' is Friday . `` Without fail , Leno 's show fills an hour and kills an hour , '' wrote The Associated Press ' Frazier Moore in a recent column on Leno 's `` Tonight '' legacy . `` For 17 years in late night he has vigorously played a game of lowered expectations , and met them . '' Ouch . Leno has never been the critics ' favorite . David Letterman , who watched Leno receive Johnny Carson 's `` Tonight Show '' desk but never Carson 's blessing , has long been touted as the King of Late Night 's true successor with his CBS show . Conan O'Brien , who began his run as Letterman 's NBC successor facing howls of derision , leaves it with some critics ' hopes that he 'll infuse the `` Tonight Show , '' his new home as of Monday , with new life . Watch how the late-night scene is changing » . And Leno ? He 'll leave behind the heavily rimshotted jokes , the Dancing Itos , the `` Jaywalking '' and `` Headlines '' bits -- all the things that drove Letterman and O'Brien fans up the wall -- with an audience of 5 million , still tops among late-night TV shows . And he 'll be moving to prime time in September . Some CNN iReporters , asked to choose between Leno and O'Brien , say it 's no contest . iReport : Whom do you prefer ? `` I feel like Jay Leno is more for men and women , '' said iReporter Melissa Fazli of Yorba Linda , California . `` Where I think Conan O'Brien , only men get . ... I do n't get his sense of humor . '' `` Jay Leno is like everybody 's cool guy to go to . You want to hang out with Jay , '' said Kyle Aevermann of Itasca , Illinois . Leno 's comedy has usually played off his regular-guy persona . In the 1980s , when he was a regular guest on Letterman 's `` Late Night , '' Dave used to welcome a wound-up Leno with a jovial , `` What 's your beef , Jay ? '' To which Leno -- who looked like a cross between a class clown and a Boston greaser -- would respond with a well-turned wisenheimer riff on being stuck in the middle seat on airplanes or evil-twin plots on television . ( YouTube is full of Leno 's old `` Late Night '' appearances . ) Moore and other critics may criticize Leno for `` lowered expectations , '' but upon taking the reins of `` Tonight '' on May 25 , 1992 , Leno opted for a more Jack Paar-esque `` Tonight '' show , mixing raconteurs among the comedians , actors and pop singers . Along with the usual entertainers -- Tom Cruise , Rosie O'Donnell -- among his early guests were opera singer Kathleen Battle , humorist P.J . O'Rourke and author-reporter Robert Krulwich . But the show , also beset by infighting between Leno 's then-executive producer and NBC brass , suffered in the ratings , often finishing behind Letterman 's CBS `` Late Show , '' which premiered in 1993 . Sources give various reasons for the turnaround -- a new set , Leno 's growing comfort , broader jokes -- but generally pinpoint the moment Leno became late night 's leader to the appearance of one guest : Hugh Grant . The actor , who was promoting his film `` Nine Months , '' appeared on `` Tonight '' in July 1995 , just after his arrest for consorting with a prostitute . Leno led off the interview with a humorously exasperated , `` What the hell were you thinking ? '' The audience picked up , and `` Tonight '' has led the late-night ratings ever since . Entertainment Weekly recently named the Grant interview the best moment of Leno 's `` Tonight '' tenure . Leno , though he 's been portrayed as a ferocious backroom infighter -- before striking a deal for the 10 p.m. talk-variety show he 'll lead in the fall , he made no secret of his willingness to leave NBC -- generally lets criticism go by like a morning mist . `` Trash talking is a part of the competition , '' he said after hearing about a jab from ABC 's Jimmy Kimmel . `` You do your best . It gives you the impetus to prove them wrong . '' And the man must be doing something right . Until being hospitalized last month , he 'd never missed a `` Tonight '' taping . He 's done 3,775 episodes , about 750 fewer than Carson , but in 13 fewer years . He still gets out on the road , recently putting on free shows for Detroit autoworkers . In fact , the criticism aimed at Leno can be reminiscent of the complaints aimed at reliable-but-dull cars . When an auto executive was asked why his top-selling vehicle -- often compared to vanilla ice cream -- remained so popular , he pointed out that although some people may find vanilla ice cream boring , a lot of people like it . Leno , a major auto buff , must know what he means .
Jay Leno concludes 17 years as `` Tonight Show '' host Friday . Leno has been criticized for dumbing down the show , but he 's been No . 1 for years . He 'll be succeeded by Conan O'Brien ; in fall , he 'll launch prime-time show .