"The Tonight Show Starring Jimmy Fallon" turned one month old Monday, which means party time!

But hold on. Let's settle down. The party must wait. First, some facts and analysis and critical perspective and quotes. Late night television has changed forever. Has it changed for the better?

To the questions:

So, how is "The Tonight Show Starring Jimmy Fallon" doing?

If the words "spectacularly well" offer a clue, then you have your answer. This launch has exceeded even NBC's expectations, and mine -- an aside offered by someone who has lived through both (and also covered) the Jay Leno and Conan O'Brien "Tonight" successions...umm, all three of them.

If numbers tell part of the story -- they almost always do -- then let's get straight to those. Last week, "Tonight" was seen by an average 4.5 million viewers at the regular 11:35 p.m. time, compared to 4.9 million in Jay Leno's last full week on the air.

That was a high-water mark for Leno -- expected for his swan song week. One of the more relevant figures is "Tonight's" performance among viewers 18 to 34 -- Fallon has around a 1 rating, or 700,000 viewers in that age group last week, compared to a 0.7 or 500,000 for Jay in his final, heavily viewed week.

Subscribe to the Entertainment newsletter By clicking Sign up, you agree to our privacy policy.

Then, finally, this number: "Tonight" has just less than double the total audience of second-place "Jimmy Kimmel Live" and "Late Show with David Letterman" -- both at about 2.7 million last week.

Thanks for the math, but what does it mean?

One month in, the math appears to have resolved the single greatest concern that NBC had going in: Would "Tonight/Leno" viewers sample "Tonight/Fallon," then return for more? So far, the answer is yes and yes.

NBC is completing research to determine how many Leno loyalists have remained, but the preliminary read at the network is that many have -- possibly even most of those who refuse to break their habit and have so far found no reason to do so.

This is a key metric because the bottom fell out from under Conan O'Brien's "Tonight" fairly quickly after his June 1, 2009, launch. Yes, this is something an apples-to-carrots comparison. "Conan" launched midsummer five years ago, and "Fallon" had a tail wind (the Winter Olympics).

Nevertheless, this is March -- a huge month for "homes using television" -- and Fallon's figures are holding up.

What is the age of Fallon's viewers?

The average age is 54, or five years younger than Leno's viewers, and "Late Show's," which is now the oldest audience in late-night TV. It's also a year younger than Kimmel's average.

Just to restate the obvious, youth rules in late night, or at least rules with advertisers -- a key reason Fallon is now host of "Tonight.' But the relative youth of Fallon's crowd indicates that his "Tonight" has actually added new viewers to the mix. Leno's "Tonight" was doing the exact opposite -- losing them.

What does NBC think?

Ted Harbert, NBC Broadcasting chairman, said in a recent interview, "I have an odd relationship with A.C. Nielsen, and deep in my heart get superstitious [when predicting ratings]. I thought we could run the table with both Jimmy and Seth [Meyers, whose 'Late Night' is also doing very well], but we didn't think it would be this high.

"My read is that we kept who we had and added more [audience], which is hard to do in any day part. That's what makes this so fascinating. It seems too early after a month to make any big general statements, but this could be one of those rare game changers where people have caught on to this guy."

Harbert -- a TV veteran and former chief of ABC Entertainment during its glory days -- says credit is due, beyond Fallon and his team, to "Lorne [Michaels], who has set this network up to be flush in late night talent."

What does the Newsday critic think?

Fallon's "Tonight" is excellent -- superior to Leno's "Tonight" (sorry, Jay, but true). Most of all, the new "Tonight" is refreshing, comfortable and often surprising, which are words seldom heard about late-night TV anymore.

This also feels like a show that knows itself -- knows what it wants to say, and how to say it, or at least how to perform it. Almost all key elements click -- the monologue especially, as well as the many sketches that made the hop from 12:35 to 11:35 with Fallon.

What's unexpected is that this really does appear to be the exact same show as Fallon's "Late Night," right down to the curtain (actually, "Late Night's" curtain was a solid blue. Fallon's "Tonight" is two-tone. Plus, that skyline). NBC and Fallon promised the same show, but how many times are promises kept in this business?

Harbert puts it this way: "The mistake we made at this network is that a lot of time was spent telling Conan how his show should change, but [this time we] said, 'You're not going to have the network telling you what to do and screw it up. Just keep doing what you're doing."

Differences, in fact, are subtle but significant: More host cross-chat with Steve Higgins, most of it improvised and most of it funny; more sketch tie-ins with members of The Roots, like James Poyser or Tariq Luqmaan Trotter, AKA Black Thought; and more monologue (but not that much more; Fallon's monologues still appear to run only around seven or eight minutes at most -- a good length for him.)

The guest segments are the weakest element, to date. Fallon's instincts are to perform, not to interrogate, so these can sometimes feel like free-form chats that lead nowhere fast. He tends to be a "fan" of everyone, has his TiVo filled with "all of their shows" or his iPod with "all of their songs."

Jimmy's a nice guy -- we know that -- but he needs to develop a critical distance and perspective. Even a coolness. That's not a bad thing when you are the host of "The Tonight Show" and therefore arbiter, or at least gatekeeper, of pop culture tastes and trends.

Has the late-night landscape changed with the advent of Fallon?

Perhaps the better way to approach this question is with another question: What about Dave?

Letterman turns 66 April 12. He is -- yes -- the second greatest late night talk show host in TV history, and also the second oldest: Johnny Carson was 66 when he retired in 1992.

The rule in television is, just to restate, ironclad -- older audiences mean reduced profits, and with younger crowds at ABC and NBC, there will also be pressure at CBS to lower its average age, by grooming a new generation of "Late Show" viewers with (alas) a new "Late Show" host.

Letterman, who has a contract through 2015, has given no indication that he plans to step aside -- or as he put it to Oprah during an interview a year or so ago: "When it’s time to go, somebody else tell me. Because I don’t know when it’s time to go.”

No one wants to see Letterman go.

I never want to see Letterman go. He is the greatest, most entertaining, most inventive late-night host in my lifetime. He is Dave. There is no other Dave and never will be.

That said ... reality is reality. Letterman will be moving along someday.

For whom? Replacement possibilities remain the obvious ones -- and Craig Ferguson is not among them. Because "The Late Late Show" host lost regularly to Fallon's "Late Night," there's appears to little chance he would succeed at 11:35 opposite Fallon again, or so the logic goes.

A shame: Ferguson's "Late Late Show" is endlessly amusing, his monologues funny and his sidekick, Geoff, probably the single finest animatronic skeleton in late-night history.

But still.

Stephen Colbert's contract at Comedy Central ends this year, Jon Stewart's next year. There now appears to be growing industry consensus that Colbert may now be the heir apparent. Is it the CBS consensus? The Colbert one?

By the way, the average age of "The Colbert Report" viewer is 43.

My kicker: Stephen Colbert could well be the next host of "Late Show."

And of course, this: We'll see.