Until the Classic Stage Company’s Uncle Vanya, I never realized that one could enjoy a show—yet still leave feeling disappointed.

For two-and-a-half hours, Uncle Vanya is one wildly entertaining play. In Chekhov’s examination of a misanthrope and the family and friends staying on the estate he runs, the title role is almost shockingly well-acted by Denis O’Hare, heretofore best known for his Tony-winning turn in Richard Greenberg’s Take Me Out and a series of musical roles (Assassins, Sweet Charity). Playing Vanya as a man too smart to not laugh at the ridiculousness of his frustrated life, O’Hare never allows the period setting to constrain his performance. His Vanya comes across as the family clown, one whose increasingly vicious jabs barely disguise the bottomless well of rage in his soul; but that clown quality simultaneously lessens the tragedy of the fate for which Chekhov seems to have destined him.

In fact, the most telling aspect of this particular production is the sense of humor with which director Austin Pendleton has imbued the proceedings. But even after the play itself stops being funny and takes a darker turn, the actors still giggle-cry their way through their scenes. Maggie Gyllenhaal, as Vanya’s beautiful sister-in-law Yelena, is particularly guilty of this crime, making Yelena a milder Hedda Gabler, a bored beauty with too much time on her hands and too many admirers. For a while, her choice works, but then Gyllenhaal is undone by her character’s soliloquy in the second act, coming across as a woman more amused by the attention paid to her, rather than bewildered.

As one of those paying Yelena attention, Gyllenhaal’s real-life lover, Peter Sarsgaard, gives the evening’s most bizarre performance as country doctor Astrov, making the besotted doctor strangely effeminate. Even a seduction scene between Astrov and Yelena doesn’t prompt more virility from Sarsgaard. Whispering “You silky weasel,” in Yelena’s ear, he immediately skitters away, as if frightened that his flirtations will succeed and an amorous woman will be on his uncertain hands.

Equally as confusing as Sarsgaard’s performance is set designer Santo Loquasto’s. Not helped by Jason Lyons’s lighting design, it isn’t until one of the characters makes reference to sitting outside that the area where most of the action takes place becomes fully recognizable as a porch of some sorts.

The only entirely successful part of a nonetheless entertaining evening is Mamie Gummer. As Yelena’s plain stepdaughter Sofya, hopelessly in love with Astrov herself, Gummer gives the production’s one truly affecting performance. Crying actual tears undiluted by laughter, Sofya is the only character who emerges as anything approaching a real person. Unbowed by her rejection by Astrov or her increasingly bleak future, Sofya gamely keeps hoping for a happy ending, despite all evidence to the contrary.

Unfortunately for Chekhov, Pendleton and company have supplied a far less ambiguously happy ending for the rest of the characters; anyone who can laugh at his own misfortunes the way O’Hare does as Vanya will never be entirely forlorn.

Through Mar. 8. Classic Stage Company, 136 E. 13th St. (between 3rd and 4th Aves.), 212-352-3101. $70–$75.