“If the Museum of Contemporary Art/Denver’s considerably smaller, more subdued building is not likely to draw every major architecture critic in the country or ignite a blaze of controversy, the institution’s leaders nonetheless have big ambitions for the $15.9 million project. Cydney Payton, executive director and chief curator, believes the structure, which opens to the public on Oct. 28, is nothing short of unique among contemporary art museums in the United States.