After much fanfare, Jimmy Fallon made his debut as host of "The Tonight Show" Monday night and, though the reviews were certainly better than those that followed his nervous "Late Night" premiere in 2009, there is still room for improvement. 

Many critics made note of Fallon's "aw shucks" demeanor (that phrase popped up repeatedly in reviews), with some finding it endearing and others less so. The Times' own critic, Mary McNamara, noted that Fallon "rigorously, and at times irritatingly, reaffirmed his signature humility." 

She continued, "Fallon has long positioned himself as a regular guy, the kind who would rather play charades with his guests than engage in lame interviews -- or, even better, just pick up a guitar and goof around. His likableness has taken him far. But even by his standards, the “aw shucks” factor was high on Monday night."

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Variety critic Brian Lowry also found Fallon's nice-guy shtick wearying and singled out what he saw as the host's relative weakness as an interviewer: "For all his skills as a performer, though, Fallon is still a question mark in terms of his ability to make magic out of nothing at the desk, the place where Johnny Carson and David Letterman thrived -- and endured. And frankly, his 'Aw shucks, I’m just so happy to be here' posture in Monday’s maiden interviews with Smith and U2 got a little tedious even before the night was over."

Others thought Fallon was shrewd for introducing himself to viewers unfamiliar with his work on "Late Night" and "Saturday Night Live." "Fallon himself made the most important gesture of the evening when he came out and basically introduced himself to the world," wrote Tim Goodman at the Hollywood Reporter. "You can't put enough exclamation points on how important and smart that was. It's such a simple and ego-less thing: Tell people who may not know who you are. If they're going to spend time with you -- and barring the Conan debacle, nobody has been there but Leno for a really long time -- they want to know something about you." 

Slate's Willa Paskin also found Fallon's first-day-at-school guise effective: "The tenor of his first episode was not 'here’s something crazy and new' so much as 'I’m a good kid, I promise, please let me take this show out for a drive.' ... Fallon is always happy to be there, always happy that his guests are there, and always happy you are there, too. But his opening bit revealed just how much Fallon and his staff understand the power -- and not just the authenticity -- of Jimmy’s ultimate-nice-guy persona."

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Though Alessandra Stanley of the New York Times was charmed by Fallon's demeanor, she couldn't resist taking a swipe at Jay Leno's older viewers by likening the new host to "a freshly licensed doctor taking over a retiring gerontologist’s practice."

Fallon's debut marked the return of "Tonight" to New York after a 42-year absence, and the city's hometown papers were divided. The New York Post's Michael Starr proclaimed Fallon's debut "triumphant" and said it "looked as if he’d already been hosting the show for a year."

David Hinckley of the New York Daily News detected some first-night jitters and predicted that, although "Fallon wasn't bad," he simply "wasn't as good as he’s going to get."

He also suggested that the real star of the new show was New York City itself, which was showcased in a rooftop performance by U2 that many critics noted as a standout moment from the inaugural episode.

"With no disrespect to Will Smith and U2, the city was his best guest Monday -- and it will be back every night. ... As the cameras slowly rotated around the roof, a clear dusk put a shimmering ripple of sunset colors behind the silhouetted Manhattan skyline. It’s a view only available here," he wrote.

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Twitter: @MeredithBlake