Stephen Sondheim's Pacific Overtures, at the Donmar Warehouse, is far more intellectually ambitious. It is about the forcible opening up of Japan in the 19th century, a theme that raises fundamental questions about modernisation, progress and the relationship of the West to the rest of the world. It is nothing if not clever, written with an artfulness that marks Sondheim's decisive move beyond the world of the conventional musical. (It dates from 1976.)

There are times when it trips over its own tricksiness. At once pastiche-Japanese and desperately ironic, it offers a Wertern attempt (sometimes serious, sometimes whimsical) to imagine Japanese reactions to the incursion of the West - and we often wonder quite where this leaves us. There is a scene in which rivalries between the Western powers are parodied by pastiches of Gilbert and Sullivan for the British, Offenbach for the French and so on. As performed at the Donmar, it seems thoroughly inept. But how far can we be sure that it isn't meant to be? What we are being shown, after all, is the "Japanese" version, the pastiche of a pastiche.

As for the work's overall impact, Sondheim has admirers in high places, including opera houses, and if I say that I often find his more demanding shows soulless and pretentious, I risk standing convicted of being obtuse and philistine. But there it is, I do. And in the case of Pacific Overtures, I found the underlying message (American imperialism bad) fairly simplistic. The opening up of Japan surely ought to provoke more ambivalent feelings.

Fortunately there are individual numbers in the show which remind you how good Sondheim can be - the macabre Chrysanthemum Tea, for instance (it is laced with poison), and Pretty Lady (a ballad about the sad mutual incomprehension of a Japanese girl and three Western sailors). The Donmar production, directed by Gary Griffin, does justice to such moments, and features some strong performances. But it also frequently guys Japanese accents and gestures, in a coarse manner which Sondheim can surely never have intended.