In just about any other show, bulging eyes denoting fear, broad sweeps of the hand to conjure invisible skylines, and self-indulgent preening during a tender ballad would be the most outrageously disgusting overacting imaginable. So why, in Gutenberg! The Musical!, do they feel fresher, more vibrant, and more truthful than most of what you see on Broadway today?

Well, you see, you have to have soul. Bud Davenport and Doug Simon might not have acting, singing, dancing, or writing ability, but they don't lack enthusiasm for the musical semi-biography they've written about the inventor of the printing press. So when they take the stage in a tiny theater at 59E59 to sell their show for what they claim is a house full of prospective producers, they pull no punches. The result is a show that leaves you bruised, battered, and (in some cases) incapacitated by the funniest jokes in any musical of 2006.

But what a way to go. The ineffable ineptitude of these two thirtysomethings as they hawk their makeshift slop opera becomes a window into the soul of dreamers and musical theatre lovers everywhere. That's an infectious, affecting, and downright comforting place to see these days, when real, irony-free musical comedies are in depressingly short supply.

That's not to say that Gutenberg! doesn't grin and wink a fair amount. But when this delightfully deluded duo do it - such as when miming moving scenery on a revolving stage, or accidentally evoking Sweeney Todd with a moralistic, hand-clasping epilogue - there's not a trace of dishonesty to be found. This is their world of musical theatre, however antiquated it might be, and they want you to help them reach it. As this worldview increasingly infuses Bud and Doug's desperation to finish their show and change their lives, Gutenberg! transforms from the funniest musical you'll see this season into one of the most heartbreaking.

But your tears will never stifle your laughter, because the show is much better constructed than Bud and Doug let on - or possibly even realize themselves. Bud and Doug are two of the prime reasons for the success of this exciting musical-comedy roller coaster, but they are - sadly - just characters created by the show's real authors, Upright Citizens Brigade veterans Scott Brown and Anthony King, and brilliantly embodied given life by Christopher Fitzgerald (Bud) and Jeremy Shamos (Doug).

The show-outside-the-show, which has been expertly directed by Alex Timbers, parodies the talentless poseurs of the theatre with the same kind of violently smiling innocence that the show-within-the-show uses to vivisect Andrew Lloyd Webber, Boublil-Schönberg, and their British pop-opera compatriots. (The score utilizes as many of these influences as incongruously as possible, to dazzling effect.) Timbers, Fitzgerald, and Shamos do more with their tiny selection of props - a box to play the printing press, a tableful of hats to differentiate the show's infinite identical characters - than many shows manage with an $8 million budget. They know that creativity, not spectacle, is where theatre truly lies.

And there's no lack of creativity here, except where it's most desirable: in Bud and Doug's show. It contains no depth or even the merest shred of believability or historical accuracy in relating its fermented fable about bravado-laden hero Gutenberg, his grape-stomper-turned-printing-press-punisher love Helvetica, and the malicious Monk intent on keeping the words of the Bible secret from the public. But the unstoppable dynamism of Fitzgerald and Shamos never seems less than newly minted: As they frantically exchange enough hats to play two dunderheaded dolts playing dozens of characters, they elevate potential shock schlock into award-worthy performance art.

Fitzgerald is flawless as the mountain-hick monk and a scream as an anti-Semitic flower girl, but wonderfully warm as barista-cum-composer Bud. Shamos's wide-eyed, confused quality is a great match for the doting Doug (who has a deliciously unrequited crush on his straight partner) and leading man Gutenberg. Both Fitzgerald and Shamos, two of our most valuable young comedic actors, convince utterly as showmen and no-men, becoming by show's end as inseparable, irreplaceable a team as Nathan Lane and Matthew Broderick in The Producers.

Since premiering at the New York Musical Theatre Festival in September, Gutenberg! has undergone a number of rewrites and refinements, all of them improvements: The show now aims and shoots more directly at its countless comic targets, and most of the weaker bits have been excised. (If you saw the show at NYMF, there are more than enough new jokes to justify a return visit.) The second act still creaks a bit, however, making it hard for Fitzgerald and Shamos to sustain a stratospheric level of hilarity for a full 90 minutes, and this even smaller theater makes it almost impossible to convey the properly cramped mock-epic sweep.

But love, they say, will find a way, and Bud and Doug, Fitzgerald and Shamos, Brown and King, and everyone else involved with Gutenberg! are joyously consummating their relationship with the musical at every performance by revealing the heart - sometimes miraculous, sometimes misguided - too often missing from it today. That's probably the easiest way to explain why Gutenberg! The Musical! is so bloody good.

Gutenberg! The Musical!
Through December 31
59E59 Theaters, 59 East 59th Street, between Park and Madison
Tickets online and current Performance Schedule: TicketCentral