Every thumbnail is covered with the game being played, the number of views, and the video length. This makes making custom thubnails difficult, since the only place to put words on the thubnail is the bottom left corner and the middle. The thumbnails could be cleaner if these only showed up when mousing over the thumbnail.
Thanks for your feedback. We will monitor this further and look at the data to see if viewers are more or less inclined to watch with the stats there.