Probably the best review Synecdoche has received so far:

"Synecdoche, NY," the alleged disaster with the unpronounceable title, is nothing of the sort. Well, the title is still a tongue-twister. But the film is not at all the surrealist muddle early detractors had described -- it's a work of profound ambition and artistry.

...Don't get us wrong -- the movie can be messy and doesn't hit all its spots. But it's funny, stylish, poignant and crammed with ideas. The last scene will break your heart.

...Distributors should be all over this movie -- not because it's attractively commercial, but because with a small edit and some savvy marketing, it could become an oddball masterpiece to rival "Eternal Sunshine." (Source)

Richard Corliss, meanwhile, calls Kaufman the saviour of this year's Cannes:

Kaufman has constructed a most devious puzzle, a labyrinth of an endangered mind. Yet it's one that — thanks in large part to a superb cast, led by Hoffman's unsparing, sympathetic, towering performance — should delight viewers who both work the movie out and surrender to its spell.

... No film with an ambition this large, and achievement this impressive, can be anything but exhilarating. Coming on the next-to-last day of a mostly glum festival, Synecdoche, New York is like a surprise happy ending. This is adeus ex machina — a miracle movie.(Source)

Thanks, Tram!