I'm gonna echo the other reviewers in my overall thoughts: the art and sound are fantastic, but there are some design decisions that make me go "wait, what?"
To start, why web-only? While I do advocate for including a web deployment to allow the maximum number of users to experience the game, I find it best to compliment it with a local install option for those who can take advantage of it. Since I was limited to the web version, it added an extra layer of difficulty because I had to fight with hotkey combinations triggering during play (Chrome's bookmark hotkey is Control-D) and occasionally encountering window focus issues.
As for the actual game, let's start with the characters: I haven't played any of the previous games in this series (it is a series, right?), so while I understand both from the game's page and the in-game dialog that Alice is a bunny-turned-human(ish), I have no idea who Umi is. Alice, for her part, looks good and acts in understandable ways, so no problems there.
The dialog doesn't seem to have a clear focus. During the introductory story, I'm given dialog choices, but their purpose doesn't seem clear and sometimes there's only one choice. When we get into the game proper, I'm greeted with a line about how to jump, then...nothing. Nothing about movement, nothing about the rabbit transformation...but then I get to an area for climbing and I'm told how to climb. OK, at least there's something. But then I get to an enemy and I see the dialog explaining attacking for a moment but it's dismissed before I have a chance to read it. And apparently there was an inventory system that I didn't know about. Even advancing the dialog is confusing: sometimes it's advanced with Enter, other times I have to click "continue."
The overall design seems to be a little confused about what it wants to be, too. Is it a tactical sidescrolling platformer a la Mega Man, where the player needs to defeat enemy obstacles while traversing short, simple platforming challenges? Is it a precision platformer where the player needs to be mindful of their jumps and learn the ins-and-outs of the control system to overcome complex platform challenges? Or does it want to be akin to a "rage game" like Super Meat Boy or Celeste where the player must learn the enemy patterns and level layouts through trial and error? The game saw me mostly just swinging from vine to vine and getting killed repeatedly, which drained my life and eventually resulted in game overs. The continue option was appreciated, but if the idea is to be a game that I learn the format through trial and error like those "rage games," why have life drain and game overs at all? The enemies were mostly non-threats; the worst ones were the spiders that threaten to knock me down as I try to get to a vine, and few of them can be defeated with an attack. Each of these platformer formats require a different structure, so if this game is going to be worked on further, I advise reviewing the format of the game, decide on which way you want to go, and restructure the game around that decision.
There are a couple of other design decisions that struck me as odd, too: one was the placement of keys for doors. The first time I ran into a locked door, I had to go through a series of platforming challenges and a small passage that required the rabbit transformation to acquire the key; the next key was placed right in the middle of the room and the door was right across from it. That latter instance is what should have been presented first, and the former would make more sense as a late-game challenge. In other words, present the player with the easy stuff first, then build the challenges up as the game progresses. The other design issue I found was the blind leaps of faith: while many of the jumping challenges are presented clearly, there are occasions where I'm not sure if I should be dashing to safety after jumping or just fall and figure out where to go next. On a similar tangent, there are some areas where there appear to be branching paths, but it's not clear if I should be going on one path instead of another and what the advantage will be. While some games have done this in the past (classic Mario and Sonic games come to mind) it would be better if these alternate paths' purposes were clearer.
I ultimately feel like this game looks and sounds good, but the design needs to pick a direction and stick to it.