TB didn't invent the concept, but he did refine it into a form that works really well. It's simply called first impressions and has been done for years in previews, etc.
The reason why his is successful though has a lot to do with the scheduling, his speaking style and his industry knowledge. Going through the F2P list on Steam would be a fine stepping off point, but to maximize success you will need to become very familiar with the Greenlight progress of games, early access and release dates. Going back and playing a F2p game that is 2 months old is a waste of your time because you've already missed the small window of search for the title. Essentially, you will need to be ready to record on opening day for a game and get that video up as quickly as you can.
I suspect that it is less valuable in the F2P space because the whole genre is designed as a try before you buy kind of thing. Whereas what WTF IS does is give first impressions of paid games, helping people decide whether they want to spend the money in the first place.