Want students to really think about YouTube videos? Try PlayPosit!
I like that PlayPosit lets you utilize (most) YouTube videos and that it allows you to write your own questions that pop up when students are watching the video. It adds a level of interactiveness that a worksheet on the side does not (actually physically pausing the video at just the right moment for reflection). The 'monitoring' or grading of the video is a little clunky, especially if you wanted to use it with a large class. Also, some videos won't upload and students experience the occasional glitch.
How I Use It
I use PlayPosit in my classes that require students to work more independently. I was able to upload and write questions for a number of introductory videos to give students a little deeper context related to what we were learning. Students find this tool useful when it works well (there are sometimes glitches or updates that make logging in, watching the video, or finding the course challenging).