What do you feel is the purpose of the graphics on the page you selected?
Small icons such as the image for home, subscriptions, queue, the bell icon, creator profile pictures, and thumbnails are visual aids to quickly navigate the website, often without words.
How well does this page meet web graphic guidelines? Which guidelines does it do especially well on, if any? What guidelines does it fail to meet?
Youtube makes sure to emphasis the thumbnails by making them big, compared to a creator's profile picture or a viewer's subscriptions, because the purpose of the website is to get many views, and thumbnails are most powerful to accomplish that as visuals pull humans in. The rest is up to the content creators and how they get an audience. Youtube itself has followed all web graphic guidelines, but some Youtubers are not the best at combining text and visually-pleasing thumbnails.