I think they are way more fun to watch than to actually play yourself.
I've watched some nuzlockes and yeah, you see all the exciting stuff and it looks great for the laughs, but one of my issues with this challenge is the part where you lose a Pokémon and have to spend an hour or two unboxing and levelling another, which isn't really my idea of fun. I prefer other challenges that don't require wasting hours grinding for every Pokémon on your team that faints.
Nuzlockers these days resort to things like infinite rare candies cheats and stuff like that, because without some kind of "help" it would be unbearable to play.
I also think Nuzlockes have kinda lost their charm. I believed one of the main points was to encourage players to start appreciating the underused and oftenly ignored "bad" Pokémon. While that might have worked in the early gens, when the options you had were a lot more limited, I don't think it applies to modern gen games that have a much bigger Pokémon variety. At the end, I don't see Nuzlockers discovering the "true potential" of Furret or Kricketune, even if their captures are limited they're still very picky about what they use and what not because they have more than enough options to choose from.