First, the downside: it's absolutely not your game if you're looking for some over-the-top, highly sexualized material to rub one out in the next five minute. This game is anything but that. Seeing you're calm enough to read the reviews, though, I can safely assume that this is not the case.
It's also a game that invests heavily on the BDSM kink and, as other reviews have mentioned, no explicit sex scenes as of Alpha 0.8.3 (and that seems unlikely to change). No object insertions (unsure if that will change in the future). No major male characters (whether that's an upside or a downside is completely up to you).
Some of the higher difficulties are REALLY unforgiving when it comes to gameplay, and it affects both the puzzle part and the more action-based part of the game, to the point it feels inadequately tested. Is everything possible on the highest difficulty? Probably. Is it enjoyable? If you're not a speedrunner AND a true masochist gamer in real life, then the answer is 95% no. The remaining 5% is for those who have such potentials yet haven't discovered themselves as such.
This brings me to what I really like about this game (and applies to all games that I've played): it serves as a journey, for both the protagonist and the player, to discover and test their boundaries to find out what's most enjoyable for them.
The game safeguards this journey by making consent an absolute element: the protagonist will find herself in a lot of spicy situations, but, unlike those Japanese eroges, there's (almost) always a way out without having to endure all the humilations and exposures she doesn't want to subject herself to. For the player, if you find the game too challenging, there's always this option of lowering the diffculty, and adjust it back when you're ready. It's not shameful to say no to whatever you find unenjoyable in your leisure time.
The game progresses somewhat slowly as the protagonist gradually accepts her true self, but slow is different than boring; rather, it's all the more arousing when you see her self-confining attitudes waver and how she gravitates towards her unrealized desires. The wanting of some more extreme treatments, the occasional dignity-saving lies and the remarks of total abandonment when she's horny...yeah, this game is by no means your go-to game of "corrupting-a-protagonist". No. She is the one who knocks.
On the gameplay side, it offers some of the most intricately designed sequences I've ever seen in games of the same genre, ones that mostly have a number of possible outcomes (and some can have up to a dozen variations if you count all minor differences!) On the writing side, the vibrant distinctiveness of characters are realized by their vivid interactions throughout the game, and there are character-defining moments in sexual contents as well.
The development of this game is steady, some monthly updates can feel a bit underwhelming as new contents can be finished in about an hour or two. If you're the free-to-play kind of person (which I assume you are since we're on this specific site) the best approach is to revisit the game once a few months so that you get the smaller updates together with a bigger update (that is hopefully there). There's another option, though: support the developers, make them economically covered to get more and better contents, and the voiceover they promised!
All in all it's a kinky gem that offers a lot, for free. What's not to love?
Edit: formatting
Edit 2: Turns out I was wrong about the highest diffuculty lacking playtest, as far as tarot puzzles are concerned. The three I've replayed all require a different (but not necessarily more challenging) solution. Solid design, would recommend if, again, you are a true masochist when it comes to gaming.