Hello! Welcome to Feedback Quest 5! It's nice to meet you! My name's Hythrain. I'm part of the FQ team and a hobbystreamer. I'm writing this review live after having played your game.
So before I get into this, since I know you can see what I score you and "hear" my reasoning, I just need to explain that my ranks for specific scores could be related to me knowing nothing. I could be wrong in my assumptions regarding the graphics and the music. If I was if you watch my VOD, please let me know.
So when I jumped into this, I was honestly expecting some sort of deep story RPG, primarily because I didn't notice you called it open world/sandbox. Going into the prologue, I had no idea what anything was. I had expected more to happen in the prologue, but instead it was just several very long fights that, I assume, are intended to let the player play with the controls. However, in terms of story it provides nothing about who these characters are or why they're important. It doesn't even tell much at all. In short, it's just empty fluff you probably don't need. Unless you plan to add that in, in which case you need to do that now. Otherwise, it makes the prologue entirely pointless.
Now that said, that's also the first complaint of the gameplay I had: the prologue fights being so long and slow for no real reason. Tutorial fights don't need to take so long.
From there, there's a massive lack of direction of where to go. Like, from the moment I started controlling my character, I had no indication where to go. I was told there was a boat but no idea of direction to go, so I ended up going the scenic route by mistake. Then when I landed, I was just as confused for this huge place I was dropped in. Then I began exploring around and immediately found myself in the middle of chaos I was not ready for. This lack of direction and just... testing out things... led to me ending up stuck in the one dungeon, where I stopped playing for my sanity (because saves). What you need is a quest log that you can use to keep track of things. In addition, you should mark people who give quests so that the player can discern who actually matters to talk to.
Otherwise, it looks cool and I'd wanna see more.