In between his masterpiece, “Falsettoland,” and his hugely popular “25th Annual Putnam County Spelling Bee,” composer-lyricist William Finn penned a very personal off-Broadway musical. Co-written and directed by James Lapine, A New Brain, premiered at Lincoln Center’s Mitzi Newhouse Theater in 1998.

Two weeks after winning Tonys for Falsettos, Finn was diagnosed with a potentially deadly vascular disease. The musical fictionalizes his surgery and recuperation, as well as grappling with the way art (and music) transcends the bounds of pain and the daily grind of life.

A New Brain received mixed reviews in its initial run, though most critics loved the score, which includes the Finn standards “Heart and Music,” “I’d Rather Be Sailing” and “Music Still Plays On.” This week, those tunes are being heard again courtesy of Encores! at New York City Center, June 24-27. Directed by Lapine, this Brain features Jonathan Groff as lead Gordon Schwinn, with “SNL” vet Ana Gasteyer as his mom and Aaron Lazar as his boyfriend.

So do the current critics still think the score of A New Brain is head and shoulders above the rest?

New York Times chief critic Ben Brantley certainly loves Groff, who “remains the go-to guy for portraying luminous pain in this affectingly sung revival.” Brantley admits that the show has “little of the dramatic tension and fully developed characters that made…Falsettos such a multi-layered treat.” That said, Encores!’ “top-flight physical production” does help stress the best aspects of the show.

In her *** (out of four) review, also lauding Groff is New York Post critic Elisabeth Vincentelli, who writes that he “keeps the production together with his supple voice and low-key charm.” Otherwise, she feels the musical has aged unevenly, with some powerful songs but a “grating childlike vibe” connected to Schwinn’s boss, Mr. Bungee.

Theatermania’s David Gordon has no such reservations. He, too, praises Groff but also finds the whole production “profoundly moving” and sees Gasteyer as a revelation. “Her simple, straightforward delivery [of “The Music Plays On”] reduces the entire audience to muffled sobs.” Gordon also lauds “hunky, silk-voiced Aaron Lazar” while noting that Josh Lamon “nearly steals the show as a randy male nurse.” Concludes Gordon, “Lapine proves once again how good he is at directing his own material.”

Not quite agreeing is Joe Dziemianowicz of the Daily News. In his *** (out of five) review, Dziemianowicz calls the production “starry and beautifully sung” but complains that “there’s an almost clinical detachment towards the characters . . . Wispy connections stunt a fuller and richer emotional wallop.” Still, the “cast of Broadway pros…enrich underwritten principal roles.”

A “big fan” of Falsettos and Spelling Bee, Vulture.com’s Jesse Green has a little less tolerance for the verbal indulgence of A New Brain. Finn “valorizes the vulgar and deliberately violative,” writes Green, so the musical’s “revue-form roots” get in the way of the story’s effectiveness. Nevertheless, parts of Brain are “terribly moving,” and the show is “directed swiftly and simply by Lapine and cast nearly to perfection,” making it ultimately “so satisfying.”

Even more admiring is AM New York’s Matt Windman. He grants the show ***1/2 (out of four) and notes that Brain gets Encores!’ new season off to “a smashing start.” Writes Windman, “the unpredictable, often catchy score alternates between madcap, hallucinatory production numbers and gorgeous, tender ballads.” He adds that Gasteyer “is in superb form” and that Groff “sings beautifully,” even if he slides over some of his character’s anxious personality.