I have managed to do all the routes in the game, including the final route. There's quite a lot to say about the VN. To start off though, let me give a rating for the game. I think a 6 out of 10 would be fairly accurate, maybe bumped up to a 7 out of 10.
It's a game that has characters I don't particularly love, but I don't dislike any of them either and I can enjoy my time with them. The themes the story tackles are engaging and I found the overarching plot to be interesting. In fact, the themes of the game might be one of it's biggest strengths...but I don't think it was executed as well as it could of.
First though, let's talk about some positives. I enjoyed the UI of the game for the most part and it felt rather fitting. Whilst I wouldn't call the music memorable, it certainly fit most of the scenes it appeared in and was utulized well.
As someone else mentioned, one of the issues that stands out in particular is the pacing of the VN. Things move VERY fast. There's constant reveals, either about the lore or the characters themselves, and there's barely any breathing room. It feels like every scene exists to deposit lore or reveal things about the characters, with very few scenes that just allow the characters to relax and get to know each other.
What's more, I noticed that once things start to get serious, the serious scenes never really stop, it's back to back with no downtime or adjustment period. The whiplash the characters can go through emotionally is sometimes startling too. Sometimes, it kind of feels like you have an idea of what you want to happen next, but you don't know how to get the characters to that point naturally, so things just sort of...happen.
I would also agree with some others statements that the character development is a bit...shallow? The main love interests have good ideas for character arcs and developments, but the rushed nature of their routes often has things coming up all at once, and it's often a lot of telling instead of showing. Honestly, the 'final' route was the best example of this, it was VERY fast. And a lot of it is quite heavy handed. I don't actually think being 'heavy handed' is particularly bad, I do think the game would of benefited from being more subtle and having more build up.
Another thing to point out is the lore behind the game itself. I understand the game after doing all the routes...but I also think the lore itself is confusing. There's various factors behind it that doesn't really make complete sense to me and whilst I understand what you were going for with the plot and the lore, it felt kinda disjointed, like multiple ideas were clashing together. It felt a bit disjointed.
The game struggled with it's foreshadowing too. Honestly, with the final route, I think the idea behind it was a good one. No, perhaps even a great one, but the lack of foreshadowing building up to it was rough. There's lots of things I want to talk about that is hard to talk about due to spoilers...but let's just say that the big reveal wasn't particularly handled very well. I'm actually kinda sad that the foreshadowing wasn't handled as well as it could of been.
And now we move onto one of the game's bigger issues...Harper, the protagonist.
This one might just be a pet peeve of mine, but Harper is such a weird character. You went out of your way to make it so he had NO appearance, to the point he's literally just a black shape in CG's, but I feel that was by far the worst way to go about it. What's more, Harper often switches between having an actual personality to having no personality what so ever depending on the scene and it's confusing. I'm left wishing that he had not only an actual design, but also that he was allowed to have more of a personality. It would of made THAT twist much more impactful instead of feeling kinda tacked on.
Let it be known though, I actually did enjoy my time with this game. I didn't find it bad, rather it was more so medicore, but it had several ideas and concepts that I felt could of made it VERY good if they were fleshed out some more. Particularly the truth behind the island.
For your first VN though, I think this was done rather well. I'm rather impressed by how well it was handled in fact. Whilst it fumbled the ball a few times, it was still an enjoyable experience and none of the issues with the game were enough to seriously negatively impact my experience. I never once thought that the game was bad or that I should stop playing.
If I was to rank the routes from best to worst, it would be
Cedar > Theo > Rown > Final Route (Which is a shame because I really enjoyed the ideas behind it, there's just very little build up and the character it focused on gets too little screentime)
For an added note though, I will admit I wasn't a big fan of the final ending. I get what it was going for but I don't think it was handled too well, nor do I think that's really the 'ideal' way for things to go. I mean perhaps that's part of it, but it felt both far too sudden and sorta contrasting to various themes of the game.