This Mandarin Oriental, on Boylston Street in the upscale Back Bay, was exactly what Boston needed. It’s not simply that it’s a high-end luxury hotel — this town’s already got a few of those — but it’s the obsessive attention to the finer points of style and design that make this Mandarin something much more than just another expense-account splurge. The payoff is in the atmosphere, which buzzes in a way few top luxury hotels can match. There’s more than a hint of the Mandarin group’s Far East heritage in the interiors, while the building itself is a modern take on classic New England limestone and brick. It’s a style that’s contemporary enough to welcome a design-conscious younger set, while still classic enough for even the most conservative elements. As for the more tangible assets: the Mandarin’s rooms are enormous, bed and bath alike, and all the equipment is state-of-the-art. The spa, with its threshold clad in intense green stone, is something almost monumental, 16,000 square feet of high-end pampering bliss.