Don't get me wrong, I've been a subscriber for a very long time, and I get a lot of great content there. But going there to watch something specific, or watching a TV series, really sucks.
I recently realized a few studios (IIRC Warner Bros and Paramount) had put a lot of content there including movies and TV shows. I decided to watch Dick Van Dyke, because I'm a Carl Reiner fan. You can't really "Watch Next" a TV show and then go in to watch the next episode. And in fact sometimes it just wants to show you the shows in a non-linear order. "I want to watch the next Dick Van Dyke" is not something that YouTube makes easy. Another example, a friend recent sent me The Chit Show, I opened the playlist of the shows, and it played them in the reverse order (which I didn't really understand until the end when I realized I was on the first episode).
Also, the YouTube algorithm for suggesting things for you to watch is really bad. It gets stuck in ruts and it's hard to get out of them.
YouTube is amazing for learning DIY things, which is a large part of why I have subscribed for so long. But for watching entertainment the whole UI really just doesn't work.