On the new Celebrity Solstice, cruisers dine in a barrel-vaulted Tuscan steak restaurant divined by superstar designer Adam D. Tihany, watch glass-art vases as they are blown at the Corning Museum's hot glass shows and walk barefoot in the grass -- literally.

Aboard Holland America's new Eurodam, they find fresh orchids in the atrium bar, spend the day in a private cabana overlooking the pool and sip Flirtinis on a low banquette in the sultry Silk Den lounge.

On the Azamara Journey, guests take tea each afternoon in their cabins from a butler whose cart carries fruit tarts, delicate egg sandwiches with cut crusts and a half-dozen teas.

And when burger mania strikes aboard one of Oceania's ships, passengers have their choice of black Angus sirloin patties topped with jalapeño cheddar and sautéed onions; provolone, roasted peppers and pesto; or -- Oceania president Frank del Rio's favorite -- braised short-rib beef and crumbled blue cheese.

All four companies -- Oceania Cruises, Holland America Line, Celebrity Cruises and sister company Azamara Cruises -- fall into a growing class of ships that experts often describe as ''premium.'' Though these ships don't have the intimacy or extras of true luxury ships -- such as lectures from former secretaries of state and fine wines included with every meal -- they do offer substantive upgrades over ''contemporary-class'' lines like Carnival, Royal Caribbean and NCL.

UK-based industry watcher Tony Peisley likens the categories of luxury, premium and contemporary to the hotel star-rating system. But with cruise ships, it's not just facilities, service and dining that matter; it's also the density -- the ratio of space to passenger. Luxury are the least crowded; contemporary the most. Premium, he says, fall in the middle.

And premium upgrades extend far beyond duvets and flat-screen TVs, found on all newer cruise ships. Carolyn Spence Brown, editor of the bible of cruise sites, CruiseCritic.com, describes premium cruising like this:

''What you should get is upgraded dining, more sophisticated dining options, interesting shore tours or enrichment. And you should get more refined service.'' Decor and entertainment typically are more subtle than on contemporary ships. ''You're less likely to find reggae on deck,'' she says.

Itineraries are more adventurous, ship size is often smaller, dining choices decidely gourmet. Robes and upscale bath amenities are standard. The average age skews to Baby Boomers and older; on two of these lines, children are discouraged.

And while these cruises usually cost more than those on contemporary brands, the price is typically half that of luxury lines like Regent Seven Seas, Crystal, Seabourn and Silversea -- a definite factor this year not only because of the actual cost, but the perception, says Tom Baker, president of CruiseCenter.com, recognized by Conde Nast Traveler as one of the nation's top cruise agencies.

''It's not the most fashionable era to be spending that type of money,'' says Baker. Many of his millionaire clients, ``are buying down.''

Just which lines qualify as ''premium'' is a matter of debate among experts. Some argue that larger liners like those from Celebrity and Holland America can't compete with the 700-passenger ships runs by Oceania and Azamara. For some, the onboard experience on Princess ships is as good or better than that on Holland America, though the Princess ships typically are larger. And what about specialty ships like the breezy, 100-passenger ''yachts'' of SeaDream, and the tall-masted sailing ships of Windstar and Clipper?