If I (somehow) got hired at Valve, I would dedicate myself to fixing Steam's deeply shitty UI. Just off the top of my head, trailer videos on Steam don't buffer more than a few seconds ahead unless you watch the entire video, and it is literally impossible to return to the exact beginning of a video without first switching away from it (you can only navigate by clicking--not dragging--the progress slider, and it lacks the resolution to go back earlier than the first second or two). And of course it doesn't recognize universal-standard keyboard commands, like Space to play/pause and arrows to navigate. They only recently let you play/pause by clicking on the video instead of on the tiny button.

Trailers for pre-Greenlight games are actually better, because they're forced to use YouTube since Valve isn't willing to invest streaming video bandwidth in them yet. It's wretched.