For most videos on YouTube, there is at least a ten minute video limit. This in itself isn't too bad, however, for some reason changes to YouTube seem to have disallowed continuous playback, meaning that if a show or movie you are watching is in, say 3 parts, YT does not jump to the next video.
This used to be something that YT provided, but does not any more for some reason. This is of course a major drawback for Leanback. For an application that will be used primarily for TV use, so that folks can watch their favorites on a big screen TV instead of a 19 inch monitor, the ability for continuous playback is needed. I for one sometimes use the videos as just straight background noise, as some might use their TVs, so to have to stop a task and hit the next video (which also sometimes doesn't show up in order) can be a hassle and I'm speaking primarily as someone on a computer, but I can imagine how annoying that would be when trying to watch through the TV.
I also found that I was unable to view uploaders through the Leanback program, instead it takes the user to the main YT website.
Another drawback I found was the need to favorite videos in order to put them in a listing that I would want to watch, instead of trying to pick through my feeds. Again, that meant needing to go to YouTube proper to do so. The upside was that they appeared immediately in Leanback, but again the downside was that they were out of order. Why would anyone want to watch part 11 first?
I think this is a major setback for YouTube.