Dramatic engagement photographs are striking and conspicuous. Plus, they're hopefully remarkable and appreciated. Most importantly, they're different.
When I'm judging photographs for online or international photography competitions, I'll sometimes comment that a photograph is "well-seen." Although that doesn't mean the photograph is dramatic, well-seen does apply to most dramatic photographs.
Dramatic portraits are usually unique as that's part of what makes them dramatic. And the surprise when first viewing the photo enhances that perspective.