There are numbers of factors involved that affect the usability of website. Only look does not matter but also functions that how easy to use website.
If we talk about the technical or functions of the website. A website should load fast, Search engine optimization friendly, mobile-friendly, grid-based, layout, clear communication, have a clear call to action buttons and should be updated to the latest technology.
Visually it should be aesthetically appealing, It should be easy to navigate, nice and clean design, respectful, engaging and honest, uses nice color scheme, choose right engaging images, right fonts, clear communication, visual elements placed to focus user attention, concentrate on what matters most.