For all but its final 15 minutes, To Paint the Earth is, at best, generically powerful. Daniel Frederick Levin and Jonathan Portera's musical about life in the Warsaw Ghetto falls into nearly every trap imaginable: too many poorly defined characters, songs that examine the Warsaw Jews' struggle against the Nazis from too safe an outside vantage point, an overall bombastic outlook and red-flagged revolutionary overtones that tend to give it the atmosphere of a woefully underpowered Les Misérables (student reactionaries and all).

But near the end of the second act, librettist-lyricist Levin, composer Portera, and director Michael Bush commit themselves to depicting an unavoidably unique story, and achieve all the moving magic that's been eluding them for well over two hours. You see then what this show longs to be, but too seldom is: a rallying cry for understanding everywhere, the desperate exhortation that horrors can always happen again.

When the disappearance of Jews within the Ghetto reaches critical mass, the painter Chaim (Scott Richard Foster) unleashes an anguished artistic cry that becomes "Paint the Wall," in which he gives visual voice to hundreds of his neighbors who have been lost to the Nazis. "See You Again" erupts from Mona (Jane Pfitsch), a captured runner for the resistance, who believes in her heart she'll return to her lover Chaim soon. The finale, "We Rise," is a stunning anthem that recognizes that even when individual battles are lost, the larger war can still be won.

Unfortunately, the preceding show is a well-meaning shambles. In portraying the vast array of opinions and efforts within the Ghetto, Levin undermines the impact of every one. The rivalry between Mona and her younger sister, Margalit (Holly Ann Butler), doesn't establish the contentious relationship they share with each other and their mother Anna (Robin Skye) as much as it detracts from the greater roles both will play. Rabbi Chernowicz (Darin De Paul) old-world bickering with his son, Euphraim (Lee Zarrett), doesn't focus the generational-conflict lens with any particular clarity. Israel Crenkov (Fred Berman) is constantly fretting over his wife Rachel (Lauren Lebowitz) and son Isaac, but since we rarely see her and never see him, bonds with us don't form easily. Even the lone Nazi on hand (Steven Strafford) is an unconvincing cipher costumed in see-through motives.

The score, too, tries to affect through disaffection, to little avail. Songs about bicycles, sewing, money, and fairy tales ostensibly symbolize richer feelings, but lack the pointed details that would forge those connections. The performers are generally little more than capable actors with this material, but are impressive singers: David Nathan Perlow makes a dynamic vocal showpiece of his nothing of a role as the leader of the student movement, while Lebowitz and Butler soar through an astoundingly belty goodbye duet, "Time," which thrills with its musical pyrotechnics. Emotions almost never explode with equivalent force.

Some of this is due to Bush's staging, which with its clumpy groupings of people and chair-heavy stage pictures suggests Miss Saigon meets Grand Hotel; and a muddy (and distractingly overamplified) sound system also pulls you away from the characters' plaintive concerns. These issues, however, are to be expected amid the rocky territory that is the New York Musical Theatre Festival, and would certainly be corrected in a fully budgeted production.

The more serious trouble is that the threat facing all these characters is far too infrequently felt. Because of the lengthy roster of characters, many disappear for scenes at a time before reappearing, making it difficult for Levin to generate suspense about who's being herded away by the Nazis. And the casual nature of so many scenes really diminishes the danger that would give them their real significance; we need to see and hear how the Ghetto is itself becoming a kind of concentration camp.

As soon as "Paint the Wall" hits, though, the show hits its stride and never drops below full gallop until it's over. It and the two songs that follow prove that Levin and Portera have a potentially great musical history lesson on their hands. But they won't unearth the rest of it until they stop painting To Paint the Earth in such broad strokes.

Tickets online, Venue information, and Performance Schedule: The New York Musical Theatre Festival