Gladio's one is fun to play, but in term of story and character development, it's not that impressive. Prompto and Ignis's ones are great though, they give us a lot of feels, and I think they are both really fun gameplay wise! I just don't like the alternate ending of Episode Ignis, but I ignore it when I replay it so this is fine :P And the Royal Pack adds many interesting stuff. The new Insomnia is particularly interesting, and it gives us the occasion to play more with the older bros, which was something that was lacking first, in my opinion. So yes, for me, they're really worth it.