While not without its merits, this game has lots of problems that make it an overall unpleasant experience. I ended up quitting my playthrough at the clay golem boss (the one that the ghost child creates).
First of all, the art is probably one of the most impressive features of the game. All of the different areas are very beautiful. Unfortunately, the effect of this is lessened by the less-than-stellar pivot based animation style. A lot of the scripted movements of the characters (for example during cutscenes) look very awkward and unnatural, which hurts the beautiful aesthetic that the art tries to convey. Even some of the movements during normal gameplay just don't look believable. It just looks like characters are sliding around on the screen instead of propelling themselves through the water (which is one of the things that makes aquatic life so interesting to look at in real life).
But what really matters most in a game is whether the gameplay is fun, so I'll focus on that now.
The game is called a "metroidvania" in the sense that, while it is a platformer, it is designed so that you spend your time exploring the environment and not being "on rails" playing through "levels". I can understand how someone who spent time playing games like Metroid would enjoy the nostalgiac appeal of that design, but I just think that, overall, it's not a very enjoyable way to spend your gaming time. The root of my complaint with the exploration is this: there's so many games out there that provide a constantly enjoyable experience, so why would you spend valuable hours of your life wandering around with no clue what to do when you could instead be playing something where you're constantly feeling engagement and enjoyment. Can you honestly say that you had fun swimming through an area that you've already seen, having to fight the same enemies, and hearing the same short music loop over and over again? If I spend an hour trying to figure out what weird action I need to do to advance the story, that's an hour I could've spent playing something more consistently fun (like Tetris, in my case), especially if the emotional payoff for advancing the story isn't very high.
I'll go into more detail on the issues with exploration in this game. A lot of the things you need to do to progress seem very cryptic, and not in a clear-cut "puzzle game" sort of way (like trying to slide blocks around to get to an exit, for example), but in an ambiguous "guess what the devs want you to do" sort of way. At the beginning of the game, it's pretty straight forward and I don't really have anything to complain about. You essentially get new abilities which act as keys to get you to areas that were previously locked (the Bind ability lets you move stones, the Energy Form lets you open Pearl gates, and the Beast ability lets you swim against currents). The way that the map works makes it obvious to you which areas you haven't explored yet, which means you don't waste much time wandering around. However, after you get all the various forms, it starts to go dowhill. Throughout the game, though, there's times where you'll waste time having unknowingly taken a turn towards an area you're not supposed to get through and having to waste time backtracking.
I only was able to tolerate the exploration by occasionally referring to a guide to make sure I was going in the right direction. I didn't want to waste my precious hours of game time taking a wrong turn to an area I'm not supposed to be at yet and having to backtrack and take a different turn towards some other area. I envy people who feel they have so much free time that they can enjoy an experience like that.
This game was praised for its music, but I'm not quite sure that the praise is that deserved. If you listened to the soundtrack by itself, I'm sure it would be enjoyable. But, in the context of the game, there's several key issues. The root problem is that the design of the music causes listening fatigue (which basically means that the music gets annoying and hurts the enjoyability of the game).
First, most of the song tracks are quite short, meaning you're going to hear the same song over and over again as you explore an area (which will happen a lot, because it is an exploration game). Second, music is played pretty much all the time. There's few moments where you are only hearing the peaceful ambiance of the water, and they are quite pronounced because they're such a relief in the face of constant, repetitive songs. Finally, the songs themselves are "loud". I mean this in the sense that there's not many moments where there's quiet parts or sparse, ambient parts in the songs.
Combat is generally frustrating. Many of the boss battles are nothing more than "swim around and shoot them and hope the many projectiles on the screen don't hit you, and eat healing items and hope you win". There's nothing really fun in that except a sense of relief when you manage to get a victory. A few bosses require you to use your various forms and abilities, and that's okay, but they still tend to be frustrating in a way that has you complaining about the design of the game and not analyzing your own tactics to prepare for the next attempt. I ended up quitting where I did because there was a bug where a projectile you needed to fire to defeat the boss wouldn't move in any direction and would just sit there where you initially fired it (instead of traveling where I was aiming), combined with a weird issue where my camera would start going crazy, and a poor design that made it so you had little window to avoid the bosses attacks. Also, you had to go through a pointlessly lengthy sequence where you build the boss every time you want to re-attempt it, which isn't fun at all. Why not just let me save before the boss is completed? Why would anyone want to waste their time doing that?
Throughout the game, the combat with the enemies isn't very fun either. A particularly glaring issue is that the screen doesn't show enemies that you need to see in order to avoid them. Some enemies will be firing fast projectiles at you or jumping at you from the edges of the screen, leaving you no time to dodge them. Simply zooming out or not having enemies attack you when they are a certain distance from you might've helped this, but there really isn't much to be done for a combat system that just involves swimming around and right clicking a bunch. A lot of the enemies take a lot of hits to defeat, so you'll be right clicking constantly during combat. Due to how movement works, dodging enemy attacks isn't very easy, even if you know what you want to do. You have the ability to do a quick dash, but I feel like the cooldown on the dash isn't enough to make it possible to avoid damage when there's a group of enemies attacking you. Precise control is also difficult using the mouse and keyboard - you either use the mouse and sacrifice precise stopping and starting, or use the keyboard and sacrifice fine directional control. Movement feels generally sluggish due to the considerable acceleration, which further hurts combat.
Overall, this game just has bad fun/minute when compared to the variety of options we have in 2014.