You can show a lot in a visual novel with your text. Not just the words themselves, but how they’re displayed on screen. Different fonts, font sizes and styles (bold, italic, etc.), even the speed and rhythm with which the words appear. Some visual novels avoid this element and keep all the text uniform, but others use the text speed and style to great affect. A really good example (though it’s more adventure game than visual novel) is the latest Phoenix Wright Ace Attorney game, which even does a good job of conveying a singing character with its text.
While it will depend a little bit on the capabilities of my engine, I do plan to work in these type of text effects in Aurora’s Nightmare. Probably not to the level of Phoenix Wright, but whenever I feel that they can really enhance the scene.