To answer the "what's the appeal" question, it's a matter of what you're looking for when you RP.
As I mentioned before, while I have never (and do not ever wish to) roleplay a canon character in-game, I've run a few canon RP blogs on Tumblr in my old fandom.
You get a very clear litmus for whether you're roleplaying your character ""right"" or not. When you're doing OC RP, this is very wishy-washy and subjective, and what's "right" is largely down to what the people around you feel like. If you're the kind of person who likes to cut-and-dry know whether you're correct, then essentially having a "brief to fill" (canon information to match) and refer back to when you're uncertain of yourself, can be satisfying. And being told "you're the closest to canon I've met" or "you play the character really effectively" is immensely satisfying, too. That's not something you can really get in the same way in OC RP, since there's no objective litmus to test your RP against.
When you make thoughtful additions or deviations, especially if they're canon-compatible or closely within the spirit of canon, then that's where you get to exercise your creativity while still being validated as "close to canon". Stuff like fleshing out parts of backstory which are vague in canon - you get to make up whatever you want. But, if it's something that ties in bits of trivia about how the character later develops and provides explanations for things which canonically have still been left vague, then it'll be praised higher by others than, say, if you make up something completely off-the-wall that doesn't really have much of a tie-in to anything.
And stuff like throwing your character into a totally different situation than they've ever been seen in, in canon, before... and still having people go "yes, this character is recognisably [name] and you're playing them really well".
And yes, the appeal is highly based off validation from other people, at least in my experience. (I'm sure someone else has a different experience.) Which is why I don't really understand the appeal of approaching people who haven't even consented to roleplaying with your interpretation of the character... of course they aren't going to appreciate it! Jeez.
As I mentioned before, while I have never (and do not ever wish to) roleplay a canon character in-game, I've run a few canon RP blogs on Tumblr in my old fandom.
You get a very clear litmus for whether you're roleplaying your character ""right"" or not. When you're doing OC RP, this is very wishy-washy and subjective, and what's "right" is largely down to what the people around you feel like. If you're the kind of person who likes to cut-and-dry know whether you're correct, then essentially having a "brief to fill" (canon information to match) and refer back to when you're uncertain of yourself, can be satisfying. And being told "you're the closest to canon I've met" or "you play the character really effectively" is immensely satisfying, too. That's not something you can really get in the same way in OC RP, since there's no objective litmus to test your RP against.
When you make thoughtful additions or deviations, especially if they're canon-compatible or closely within the spirit of canon, then that's where you get to exercise your creativity while still being validated as "close to canon". Stuff like fleshing out parts of backstory which are vague in canon - you get to make up whatever you want. But, if it's something that ties in bits of trivia about how the character later develops and provides explanations for things which canonically have still been left vague, then it'll be praised higher by others than, say, if you make up something completely off-the-wall that doesn't really have much of a tie-in to anything.
And stuff like throwing your character into a totally different situation than they've ever been seen in, in canon, before... and still having people go "yes, this character is recognisably [name] and you're playing them really well".
And yes, the appeal is highly based off validation from other people, at least in my experience. (I'm sure someone else has a different experience.) Which is why I don't really understand the appeal of approaching people who haven't even consented to roleplaying with your interpretation of the character... of course they aren't going to appreciate it! Jeez.