Certain exhibitions split a critic's personality right up the middle. "Palace and Mosque: Islamic Art From the Victoria and Albert Museum," the show that opens Sunday at the National Gallery of Art, is one of those.

First up, the critic as a mean old Mr. Hyde.

Shows like this, says Hyde, are lame-brained ways to fill temporary exhibition slots and pull in unsuspecting summer visitors. First, you borrow all the objects, quick-and-dirty, from a single foreign collection that's undergoing renovation -- such as the V&A's Islamic rooms. Because you don't have your own experts on the subject, you get the lenders to throw in organizers, too.

For some reason, that then means you can forgo the kind of heavy-duty research you'd expect from your own curators as they scour the world for the crucial objects needed to make some kind of coherent point. You're happy just to get a cheery kindergarten trot through a few attractive gems of foreign art. In these summer shows, there doesn't have to be any coherent argument advanced or some important issue to work through: "Greatest Hits From Timbuktu" is good enough.

And if you're really lucky, some day your public -- and your funders -- will start to see this kind of thing as normal and let you off the hook for doing the more substantial kinds of shows that take time, and travel, and foreign loans, and money to put together. So long as a show is good-looking, they'll stop caring if it happens to be empty-headed, too. You'll be able to lose some of those brainy curators and hire an extra marketer or two.

And then there's the real Dr. Jekyll me, thoughtful and open-minded to a fault. Jekyll's first impression, on walking through a show like this, is that there's plenty of good-looking art in it.

There is a slew of impressive calligraphy. Some is in books -- the Koran especially, of course -- where the gorgeous writing is at the service of the words it spells out. Some calligraphy was valued for the sake of the penmanship itself: There's a great scribe's practice sheet, carefully mounted and preserved by an admirer as an independent work of art. And, in this show -- all of whose objects come from a museum of craft and design -- most of the writing is used on decorative objects of one kind or another.

There is a wonderfully bold tomb inscription from Uzbekistan, in deeply carved ceramic tile, that makes the wall it sits on come alive.

There are exquisitely delicate glass vessels, and heavy ones in brass, whose surfaces crawl with a calligraphy that's as much about ornament as about the phrases it conveys.

It's worth remembering that for many of the peoples who embraced Islam over the 1,000 years covered in this exhibition, and who helped spread its influence from China and India to Spain and Hungary, the Arabic language and script started out as foreign imports.

The decorative potential of Arabic letters must have come across more strongly to them than to a native speaker, who would have read them first for meaning and only later for their look. A storage jar made in Egypt or Syria, when those countries were under the rule of the Turkish Mamelukes, has "calligraphic" decoration that doesn't spell out any words.

So does a plate of ceramic lusterware from Iran, the Persian-speaking land that became one of the great centers of Muslim culture. And the "Moresque" metalwork made during the Italian Renaissance often had pure nonsense writing on it, borrowed from Islamic art for style instead of substance.

Of course, it's hard to know if a fabulously cursive Arabic script helped build a taste for twisting ornament, or if it was that taste that helped sell fancy letterforms in the first place. In the later 15th century, Ottoman woodworkers covered a 25-foot-tall wooden pulpit, known as a "minbar," with starbursts of geometric inlay that easily out shout the few inscriptions also carved in it. (Maybe the inlay was meant to tease the congregation's eyes while the preacher's ornate rhetoric appealed to their minds.)

One of the few near-constants in this exhibition is a love of over-the-top ornament. The textiles, especially, are breathtaking.

I'm jealous of the little Turkish prince who got to wear -- and was buried with -- a little golden caftan with a blizzard of red flowers woven into it. It only underlines how preposterously drab we've let our clothes become. And it's no wonder that a prelate in medieval Europe had his robes done up from a blue-and-gold silk cloth made in Mongol-ruled Iran. In 1300, how many European craftsmen could have matched the pomp and technical perfection of its woven garlands, oxen and pelicans? (The many animals and human figures in Persia's Muslim art counter any notion that the Koran's few words against idol worship put the kibosh on representation. Muhammad also came out against silk robes, but that didn't seem to put much of a brake on Islamic haute couture.)

Then there's the V&A's great "Chelsea carpet," also woven in Iran but in the 16th century. It makes you realize why such "Persian carpets" have epitomized extravagant good taste for centuries. It is hard to imagine a more impressive, luxurious floor covering. There aren't many other works of art that strike such an absolutely perfect balance between a clearly legible overall composition and an overwhelming wealth of local incident. It's as though a rug such as this was carefully considered to please a visitor's first glimpse on entering the reception hall, as well as the lucky guests already sitting on it and getting a closer look and feel.

The Chelsea carpet also teaches a crucial bit of history about Islamic art: There are pictures of elaborate Chinese vases woven into it, and they indicate how willing Muslim culture always was to borrow from the peoples it brushed up against, as well as to ship Islamic goods and culture out to them.

Some of the most impressive objects in the exhibition are made of patterned white ceramic: There's a footed bowl, made in Ottoman Turkey in the early 1500s, covered with spiraling garlands that are almost hypnotic. But such great works of Islamic "fritware," as it's known, were only born from competition with the imported Chinese porcelain most valued among Muslim connoisseurs. It looks as though the famous blue-on-white decoration that Europeans came to think of as traditionally Chinese first appeared on Near Eastern earthenware, then was copied by the Chinese in porcelain to appeal to an Islamic export market and only later recognized in China itself as something to appreciate at home.

There are dozens of other exquisite objects in this exhibition, spanning so many styles that there's something here to suit nearly all tastes. (If there's any message to take home from this show's crash course in "Islamic art," or from its useful little catalogue, it's that the category itself doesn't get you very far, any more than the category "Christian art" could make much sense of all the objects made in Europe since the birth of Christ.) But -- and here comes bad old critic Hyde again -- the visual plenty on view in this show should be the minimum you can expect from any exhibition, rather than the best you're likely to get out of it.

After all, at a museum as good as the National Gallery, it's not as though the alternative to a show such as "Palace and Mosque" is a show that's full of ugly, uninteresting art. The researched shows its curators have organized in-house, with some point to make or some issue to explore in depth, have never included fewer entrancing objects than a lighter show would have. But carefully conceived, coherent exhibitions will have brains as well as beauty; they can mean something to both the greatest expert and the most casual observer. There is a chance, that is, that they might matter in the long run, rather than just pleasing a few laymen -- such as this Dr. Jekyll critic -- on some lazy summer afternoon.

Palace and Mosque: Islamic Art From the Victoria and Albert Museum is on view in the East Building of the National Gallery, on the Mall at Fourth Street NW, from July 18 to Feb. 6. Call 202-737-4215 or visit www.nga.gov.

A boldly carved inscription on a tile from a tomb in Uzbekistan, carved about 1360, is part of the National Gallery exhibit. A glazed tile from Turkey, above, dated 1727, bears an Arabic script-inspired calligraphic design. A brass tray, below left, made between 1314 and 1363 when the Mamelukes ruled Eqypt, also is heavy with inscriptions. A footed bowl from Turkey bears dazzling geometric designs.