If I wasn't sick before, I would've posted earlier because this is one of those things I love to talk about. As for customizable characters, I think it's a neat idea, and works for games like Splatoon where story isn't the strong point, but I'm generally against it. It's warmed up to me a little bit after FE Awakening and Fates, but then games like Xenoblade X completely change my mind again about it. There's a big difference between the two: one has a silent protagonist, while the other does not.
I'll start with the silent protagonist. This probably has to be one of the most overused tools in terms of making the main character. Generally, it's used so that a player can reflect what their character is doing or saying and even sometimes gets the options which also helps with the immersion. The problem is also part of the solution. What if you don't immerse yourself or reflect yourself onto your character? Most of the time, it's actually nothing more than an empty husk or not really a person with zero personality and actions that really don't alter the story that much (in Reborn even, it's the other characters that really drive the plot. Think of how many instances outside of gym battles, where the player is alone facing a villain or a single character...especially toward plot driven events). In other words, how can a feel for a person who really isn't a person?
There are some really good silent protagonists in RPGs though (and other games). One of the better silent protagonists is Mario. In Mario RPG and the Paper Mario series (along with the Mario and Luigi as well) you can actually get a feel for Mario's character, despite the fact he doesn't talk. In fact, it'd take away from his character if he could because he actions are just so well done (he even does a reenactment of his encounter with Smithy which is hilarious). Metroid is another one that while Samus can talk, her situations show are isolated meaning she has no reason to talk. As you can see, it's a very situational thing but it's usually better used for a "weaker" story or more actiony games. Though one character that counter this arguement is Lucas from Mother 3 but that's a different story.
Now I'll get into a protagonist that can talk. A big fault here is that customizable characters generally have a bland or generic personality, but the fact they can talk really does make them more human. As a general term to writing a story, the main character should be someone the readers (or players) should be able to connect to as well as be someone enjoyable to watch as they go on their adventure. Believe it or not, that's easier said then done. I could probably make a list of bland, boring, or horribly written protagonists found in games which is why it's not uncommon for someone's favorite character to not be the main protagonist.
I prefer talking characters as their actions do affect the story vs a silent protagonist who generally has little impact (or is a chosen one) in terms of story. Is Shulk a better character than Cross (the Xenoblade X avatar)? Yes, because we know about his beliefs and how they different from a couple characters. Here's a quick way to understand my thinking: make a list of all your favorite protagonists and see how many of them are actually custom characters. Custom characters rarely help with building a long or grand story such as the Xeno Series, the Tales of Series, or the Legend of Heroes Series who have some great speaking protagonists.
Now I think Thomas brought up a really good point about a movie and a video game. I agree with it in that watching a movie would have a pretty similar experience if a video was always about the main story. Video games are rarely so straightforward. There's side plots, quests, and a whole gameplay mechanic that'll make you a bit more involved vs just sitting and watching a movie which is why I prefer them, especially with long stories. A majority of them are about exploring a world the creator created when you get down to the finer details.
But if you want me to simplify that complicated answer: For story purposes, I dislike them for the most part, but for gameplay, I actually prefer them which is why I say it's very situational.
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As for the fourth wall, I don't care for it honestly. I mean it'll get a good laugh or can be done really well, but it's not something I look for. I know undertale has quite a few, but I haven't played that game so I can't judge it.