Contrast, Drama and Climax
All excitement emerges from contrast. Information is contrast, and the power of the contrast determines the gamut of the information, so, in an artwork, greater contrast is always better. Informationally weak genres, such as minimalism can be seen in contrast to their surroundings. Minimalism makes an impact emotionally because it contrasts the noise of the world with its relative peace.
There are two types of drama which work in all arts; music, drama/film, poetry, visual art: climax and conflict.
Climax
The first builds up to a climax, a switch or dramatic conclusion. For his films, Alfred Hitchcock thought of one scene that would sum up the whole story, then steer the narrative towards it. This was the climax. Climaxes need drama by having opposites to create a rapid release of tension.
Climaxes should also be expected, pre-empted to the audience, because anticipation of an inevitable dramatic event extends and amplifies the emotion. Imagine a riding rollercoaster and the effect of slowly climbing the steep hill, all in anticipation of the sudden drop, the growing sight of the world from such a great height. The initial fall from the peak might be the moment of climax, but to start there would kill the emotion; the anticipatory climb is essential.
In music, a theme might build towards the climax, or in writing it might represent a reveal. In classical drama the climax is about 75% of the way through a work. Almost all Hollywood films follow this structure, and many songs. Dream Home Heartache by Roxy Music is a paragon of climax. Sheer Heart Attack by Queen has the climax at the very end. Many symphonies build to climactic moments; Beethoven's 8th builds to a dramatic recapitulation of the initial theme. Sibelius' 5th instils calmness by repetition which grows to a climax that is subverted by its unexpected ending. I never liked the ending of Sibelius' 5th symphony. It sounds silly, it seems to stop taking itself seriously. I can barely listen to it and always imagine a more conventional, extended chord or two. Perhaps the ending the composer chose annoys me because it is too unexpected? Perhaps a more typical ending would have been too boring for him?
Conflict
The climax structure isn't a new idea, it dates back to ancient Greece. In the 19th century the Swedish dramatist August Strindberg wanted to break apart this structure and created new work based on two opposing forces that fought throughout. Beethoven's 5th symphony begins with its climax, as does Bach's Toccata and Fugue in D Minor, so the power of these works is not anticipation of a single event. Ingmar Bergman's films were influenced by Strindberg and have conflicts throughout to explore the theme. The aim here is a clash of forces that intertwine and wrestle.
The key element is always contrast, the greater the opposites, the more powerful the drama. A pop album might be well structured and unified in feeling; Kate Bush's Ninth Wave for example, without a climax because it is filled with dramatic opposites.
Thema
A theme is a repeating structure, and in both climax and conflict, a unifying theme is important because it is a way to manage expectations. Poems rhyme for this reason, the reader can feel what is coming and this feeling can be rewarded or subverted. In a climax, several smaller climaxes might grow towards the primary one, and like the rhyme in a poem, the large one needs to be expected for the best effect, and so should ideally be similar to something experienced before.
Mike Oldfield's Tubular Bells would have been more unified if the climactic bells part was at the end and reflected the theme that opened the work. In that way, this long work would have been a path of expectation. Oldfield did this with other works like Amarok and Ommadawn.
In visual art, theme, drama and climax can be difficult to command because art is instantaneous. When we see a painting in real life, on the wall in a gallery, we experience it in many ways. The painting might be alone, but more often among a swarm of other paintings, and we are often with a swarm of other people. The ideal is perhaps seeing a painting when we are alone, and when the painting is alone; a solitary dialogue. Even in these ideal circumstances we don't look at the whole painting at once; human eyes dart. The artist must manage expectations so that different parts are seen in different orders to create clashes and rewards. Climax might be the dominant form in drama and literature, but conflict must be the dominant form in visual art because of the lack of control over what the viewer sees and when, and this limits the control an artist has over expectation. Time is important in art, it's difficult to feel anything in a flash.
It's difficult to manage expectations in visual art, and the effect will probably depend on each viewer, as well as the thousand other circumstances in which a painting is seen, but this doesn't make the artists job hopeless.
Knowledge, presentation, expectation. These are crucial factors when displaying, and absorbing, art of all sorts, but they are especially important factors in non-temporal art like painting or sculpture, versus music or film. Literature is somewhere in between these.