General design
It's a dark and masonry-based theme that helps you exhibit your portfolio prominently. I can say that the simpleness of the design makes the reader focus on the content and photos rather than being distracted by other elements.
Other elements
The author uses the black color as the main tone to create a mysterious feeling and highlight the images. The black background can be changed in the Customizer so don't worry if you don't like this dark style.
Montserrat and San-serif are two family fonts used in XI Portfolio. Because the author wants to prioritize the images, he chooses the very straightforward and basic font.
The masonry structure can help to save the space and arrange the posts in a flexible layout. But in this theme, I find a mistake with this structure when the images have different sizes like this.
Mistake with the masonry structure
Plus, the spacing between the images is dissimilar, so it looks quite unsymmetrical.
The dissimilar spacing
The most intriguing feature of the design lies in the portfolio section. When you click one image, full-width version of if appear so stunningly in the form of a slider. This slider allows you to quickly move to the other photos continuously.
The other elements are extremely simple like the full-screen menu, header, and footer. There is even no sidebar anywhere at all. I think that it's a wise design to boost the concentration on the images and content.
Responsive
I use this free WordPress theme in many different devices like smartphone and tablet. I'm so satisfied that the design looks good in all screen and viewport without any problem.
The responsive design checked by ami.responsivedesign.is.