Judgements of aesthetic value rely on our ability to discriminate at a sensory level, but they usually go beyond that. Judgments of beauty are sensory, emotional, and intellectual all at once.
According to Immanuel Kant, beauty is objective and universal (i.e. certain things are beautiful to everyone). But there is a second concept involved in a viewer's interpretation of beauty, that of taste, which is subjective and varies according to class, cultural background and education.
In fact, it can be argued that all aesthetic judgments are culturally conditioned to some extent, and can change over time (e.g. Victorians in Britain often saw African sculpture as ugly, but just a few decades later, Edwardian audiences saw the same sculptures as being beautiful).
Judgments of aesthetic value can also become linked to judgments of economic, political or moral value (e.g. we might judge an expensive car to be beautiful partly because it is desirable as a status symbol, or we might judge it to be repulsive partly because it signifies for us over-consumption and offends our political or moral values.)
Aestheticians question how aesthetic judgments can be unified across art forms (e.g. we can call a person, a house, a symphony, a fragrance and a mathematical proof beautiful, but what characteristics do they share which give them that status?)
It should also be borne in kind that the imprecision and ambiguity arising from the use of language in aesthetic judgments can lead to much confusion (e.g. two completely different feelings derived from two different people can be represented by an identical expression, and conversely a very similar response can be articulated by very different language).