I wrote a comment here a while ago after finishing TJ as my first route, and I'm returning now after finishing all of the routes to correct some mistakes and write a definitive review of the best visual novel I have ever played.
I will try to keep this review spoiler free until explicitly written otherwise.
My point from the previous comment still mostly stands:
To have the best experience, you should follow the recommended route order.
Playing out of order is definitely a possibility, but can be (at least in my experience) confusing because the latter routes expect the player to know stuff. Though still, as other people here are saying, the route order doesn't matter that much if you finish all the routes, so feel free to go with your gut.
I searched a bit and most people seem to agree that Carl->Leo->TJ->Flynn->Jenna is a good order, which I do not object, but would like to elaborate:
(I should note that it is also the order in which the routes were written)
Carl's route does not need any context at all to understand, so easy first choice.
Route 65. This is a small prequel game that will be referenced in Leo's and Jenna's routes. It's good if you play it, but it may be skipped as it doesn't really add much to the table that isn't already in their routes.
Leo and Jenna could probably(?) be switched, but I think Jenna's route explains quite a bit more stuff than Leo so we're keeping her for the end. We're keeping one of these routes for last because these have the most satisfying good endings.
TJ and Flynn could also be switched, as they both circle around simillar plot points, but from different viewpoints.
Before starting the game, you should also play the short side stories (click on the lake in the menu, then the broken window and then scroll down to Chase). Even though they are well hidden, they will be mentioned quite a bit in the game.
Thoughts on the game itself
The game may seem very generic at first. But it quickly gains momentum as the friend group gets into an argument because of an old incident at the lake, where one member of the group had drowned when they were kids.
You then have a choice to follow each of the characters and their vastly different experiences around the town following the incident.
You will feel a lot of emotions playing this game, be it delight, contempt, confusion, sadness or lust (and believe me there's a lot of the last two), but you will never feel boredom because the plot always manages to move along without feeling sluggish.
You should definitely play the game if the idea of psychological horror sounds even a little bit interesting.
I also need to say that I absolutely LOVE the way the situational illustrations (like shown on the top of the page) are drawn, and I am absolutely bewildered how perfectly these images depict the feelings of the characters and the situations. One moment you are looking at a generic background, imagining the scenario before you, and the next you are looking at an image perfectly portraying it; the feeling of cold, dark, unsettling, yet somehow slightly warm melancholy with a hint of familiarity, a deja vu.
After seeing some of the images, I sometimes spent a while just looking at them, collecting my thoughts and thinking about how good and elaborate this game actually is.
Thoughts on the endings and story (MAJOR SPOILERS)
Carl - Even if Carl's route is the very start of this journey, it shows very well how the game is/will be: your friends are haunted by something, you're just a plaything to it, and if you decide to humour it, it will not end well.
His good ending was surprisingly wholesome, with Carl turning his life around because of the experience, but there was still a hint of bitterness because of the lack of any information about what happened to the others while we were hallucinating.
His bad ending was very brutal, just the way Carl was depicted at the end broke my heart, a common theme that happens in all the bad endings.
Leo - Again, wholesome good ending, but there is always that neverending bitterness, that feeling that you could've done more, better.
His bad ending was very, very well depicted. The whole way it felt like a bad dream. "There's no way this is happening, or is it?" The way all of it happened left me speechless, which also is also something very common (at least to me) across all the bad endings.
TJ - This one is a doozie. It was the very first ending I have finished, and it just left me baffled and insanely confused. I decided that it would just clear itself up later and finished Carl and Leo before attempting TJ's route again, and I must say... I am still confused. (I even replayed the ending while writing this review just to make sure I am not overexaggerating)
It's not the murder itself that is confusing to me, but rather the aftermath. The scene in the car just feels... like TJ isn't actually himself. Yes I do know that Chase's perception is absolutely fucked by now, but when TJ smiles, it just doesn't seem like him at all, even if it'd be dishonest.
This route also feels much more real, if that is the correct word, than the other routes. Leo, Jenna and Flynn have monsters, Carl has possesions but TJ only has Chase's Hum-induced schizophrenia, which just makes it so much more unsettling than the other endings.
Flynn - He didn't deserve it. That is all I could think of when I finished his route. Getting killed by Chase in TJ's route may be one thing, but to have everything ripped from you after everything seemed to be going fine, only to then be thrown hundreds of meters underground to burn to death, THEN while that is happening to also hallucinate about all the horrible things that happened in Echo, AND THEN TO FUCKING TOP IT ALL OFF he gets turned into a monster that isn't even fully him, gets completely removed from his timeline and then has to watch all the horrible events happening in Echo. Like WHAT THE FUCK?! This is probably the worst fate of a fictional character that I know of, and I know of quite a few.
Jenna - Thank. Fucking. God. that I followed the recommended route order, because if I had to end it on Flynn I would be crying for a few weeks. Jenna's route has 2 good endings depending on how you see it.
The first good ending ends with what everyone wanted to do when the histeria started: get everyone away from Echo. There is of course Echo's slight feeling of bitterness™ because of the call that Flynn got (which I assume is about the death of his aunt), but other than that everyone is safe and sound.
The second good ending is very bitter, where Chase unintentionally(?) manipulates Jenna into indirectly killing Heather and then flooding the entire town. This may seem pretty bad at first, but remember that the Hum always returns, and Jenna essentially managed to break the cycle and saved countless lives. It it not good for the friend group, but it is basically the "for the better good" ending. Nobody will ever get hurt again, but it cost a few lives and releationships to get to that point.
TL;DR
Carl:
G. - very good start for the game
B. - heartbreaking
Leo:
G. - Wholesome w/ a hint of bitterness
B. - Felt like being in a nightmare (compliment)
TJ:
B. - Confusing, heartbreaking and surprisingly realistic
Flynn:
B. - Worst fate of a character in any fiction I've ever heard of. He didn't deserve that!
Jenna:
G. - The ending that everyone wanted
B. - The ending that everyone needed
Final Thoughts (No Spoilers)
As mentioned at the begining of this novel-sized word dump of a review, the game is good, though I don't think I need to tell that to you if you managed to get this far down. If you didn't play it yet, play it! If you did, then heck, play it again! It's free! The download button is right there! Now click it and step into that emotional rollercoaster.
This is probably as good as any visual novel can get; the worldbuilding is very extensive and interesting, the characters are relatable and well made, and the artwork, fuck, the artwork fits in absolutely perfectly. 10/10