I've purchased about 150 courses from Udemy, from a number of authors, and with Rich Rost, he is by far the best instructor I've encountered online. He's got a very clear voice, his methods are logical and easy to follow, the videos are top notch, he's the best. An important attribute is his videos are not wordy to the point of boring. Most are fairly short though he references a lot of his other videos that are helpful for understanding whatever the topic being discussed is. The only requirement is a small knowledge of sci-fi movies and shows.