The thing I find that is lost is the blurring of the line between video game and animation. Homestar Runner cartoons were often interactive, they made several outright games but also the things that were closer to animations often had easter eggs in them, from (in Strong Bad’s words) dumb stuff that would pop up to entire extra scenes.
Early Youtube had a thriving animation community, but given the limitations of video-based content they really couldn’t do those interactive elements, then Flash died, and now that culture is basically gone.