Okay, so I played it too. First, let me preface this by saying I mostly agree with Correojon's points, so I'll try not to repeat what they said. Also, usual feedback note: while I have somewhat strong views on some design stuff and may offer suggestions, they're only my views/experience and you're perfectly free and welcome to disagree!
With that said: I'll admit, my overall feeling isn't very positive, and if I wasn't testing, I'd have dropped off just before/after the red mage fight. I believe you have a solid mechanics foundation (I had some play issues I'll go over below) but I was kind of put off by too many presentation elements to be invested, and care about what I was doing.
-First of all, the keys: it's a standard and many don't bother, but it's still appreciated when ZQSD (international version of WASD) works in parallel, even when keys are ultimately meant to be remappable. I'd suggest moving them to ESDF (no change in international layouts) or even better, the directional arrow pad (or both). Using the HJKL keys for the other interactions also felt a bit cramped: even though I get the reference, I very quickly moved them to the numpad so my hands could be more comfortably apart.
-Trying to remap some keys to the numpad additional signs (+, -, *, etc) led to some confusion as they would not display correctly in the key config menu, so I wasn't sure if they registered, failed to register, or was even attempting to input anything anymore.
-Even though this is a metroidvania and you get the jump boots fairly quickly in both tutorial and adventure modes, I fely very limited and constrained by the initial jump arc. It's very small and has limited air time, making for uncomfortable air control. I'd rather feel empowered by finding hi-jump boots, rather than think "ah, finally I'll be able to jump somewhat adequately".
-the camera felt a bit stiff, as it keeps the character at the center of the screen at all times. While it's a much more difficult problem to handle in a metroidvania game, considering players will want to go left/up/down/right at all times, there are still a number of different ways to approach moving it to offer visibility: if you haven't already, I recommend checking out articles regarding 2D platforming cameras like this:
http://subtractivedesign.blogspot.fr/2013/02/making-platforming-games.html
http://www.gamasutra.com/blogs/Itay..._and_Practice_of_Cameras_in_SideScrollers.php
http://www.gdcvault.com/play/1022243/Scroll-Back-The-Theory-and
http://www.imake-games.com/cameras-in-2d-platformers/
(if your intent is to go the "fixed camera" route, then I believe some of the enemy/trap placement in adventure mode should be reworked based on where the camera actually is when encountering those challenges)
-Using "down" to interact is counterintuitive, especially considering all elements appear to be behind/above us, so "Up" feels completely natural (and is most likely why it turned into the current standard). In addition, this being a platformer, Jump/spacebar is the most frequently used key, yet it can't be used to skip text boxes. Every instance of text box had me pressing in succession spacebar (doesn't work), enter (doesn't work, some confusion as it's the key used in the main menu) then frustratingly remembering to press down.
-regarding the tutorial textboxes, they don't appear long enough: I believe they're commanded through triggers (one "appear", one "disappear") that are much too close, forcing you to stay still if you want to read the rather long messages in their entirety. In that kind of scenario, I like to read while moving, which was simply impossible here, as the windows closed almost immediately after I took a few steps. They also kept popping back up when going back/messing around, making for visual clutter.
-coming back for the "lungs" item in the tutorial area: while a good idea in theory, the fact that all old tutorial messages still popped up when going back all but indicated that we weren't meant to go back. You could argue this makes actually going back and finding the lungs all the more sweet, but I think the constant text box visual interruption was more grating than anything else. I'd recommend all tutorial messages on the way back be disabled after reaching the yellow statue (possibly even one of them replaced to hint that "hey, going back is actually something possible), or if you're concerned that players still need to access them to relearn what they saw coming in, you could tie them to computer terminals the player would have to interact with (and go one step further, and add a delay timer to their disappearance, so you solve both the trigger appearance issue, and the going back one).
-all text boxes appeared the same, even though some of them are actually multi part? Unless I missed something, I would have liked a small indication that there was more text coming (a small arrow, a (1/3), anything - one of them, the first in fact, had a (...) which at first I thought was the end of the message, which was confusing for a bit, but the later ones didn't reuse it). In most cases, I believe having context as to the amount you're reading/about to read is important when factoring in the information a specific text box is giving you.
-During the adventure mode introduction (again, unless I missed something) there are no hints that the world is set in a different universe (even magic is arguably a "regular" fantasy standard) until we reach the "remote village of humans" line, which made me have a double take, as it felt very unnatural to refer to anything that way, both in regards to what I understood/assumed the character to be, and the information I had up to that point.
-In general, I wasn't feeling the writing: for lack of a better word, it felt slightly standoffish, and most characters weren't imparting very useful personality or information - kind of like Castlevania 2 with better grammatical structure. Most notably, a huge deal seems to be made about racial tension, but that didn't seem particularly well handled, and I didn't care for some of the terminology and attitudes of several characters (first woman character you meet calling you "handsome", first "non humans" you meet being dismissive/agressive and territorial even though they live 3mn away from the human settlement, etc).
-right when starting adventure mode I went left, and I tried for a while to interact with the boat to cross the lake, as it had an elaborately detailed engine. If it's to be a piece of scenery, I think it's slightly *too* elaborate, as it gives off vibes of being interactable (possible later down the line with items/powers, I don't know?) - either way, as a "first impression" towards possible interactions, I felt frustrated I couldn't do something I thought was visibly hinted at. (admittedly, the tutorial said objects would glint, but since it also encouraged exploration and trying things out that were visibly "not intended", I assumed this was another case of obfuscating information).
-during playing, I didn't feel much sense of progression: the later jumps were just as hard/wide as the beginning ones, and the enemy strength varied wildly, with the initial snails being effectively harmless, then running into a super tough plant with a million health, and then bees that could be taken down in two hits. This is the part where I mostly agree with Correojon: I believe the current level structure lacks progression, which ties into the "integrated tutorial" discussion. I also believe having an explicitly integrated tutorial isn't a good idea, but I didn't think that was what Correojon suggested. I believe what the LD currently needs is introduction to the different mechanical concepts solely through play (no text explanations, no nothing except the act of play) and get the player to overcome slightly increasingly challenging obstacles before presenting them with "jump over fireballs with super low ceiling heights" and "jump off an elevator near the top of the screen with spikes on top when spikes haven't been introduced before and the screen actually doesn't show the top soon enough". Think back to the intro stage of Megaman X and how it gradually presents you with challenges that use the different buttons/combinations of buttons, all without uttering a single word.
-the player hitbox felt larger than the character (it's likely just the outer bounds of the sprite, but it "feels" larger because of reaction time) and I got hit a number of times by bats and the red mage even though I was "visibly" away from their range. If it's not already in, I'd recommend making the player's hitbox and enemies hurtboxes smaller than the sprites outlines, so there's a degree of leeway for player reaction time, and also create a satisfying sense of "narrowly escaped that one" when brushing very close to enemies.
I'm very sorry I'm not more enthused, as it's clear a lot of work already has been put in there. For reference, my closest point of comparison would be La Mulana, which is not a good thing in my book (I find it purposefully obscure to the point of being voluntarily frustrating, and not in a good way). Challenge is one of the things I'm least interested in in a metroidvania game - this may be where our views diverge the most. Still, I believe "challenging" requires to be "fair", and purposeful obtuseness goes the opposite way AFAIC.
However, I also believe you have very solid mechanics, and my issues mostly stem from their use and presentation, and this being a test/prototype version, I'm not sure how much of it is actually placeholder - I would likely have a very different take on another level design using a different script/writing style. I'm also of course clearly looking to design a platformer of another type in regards to camera usage/jump hang time and the likes, so we may have wildly conflicting design philosophies here :-D
I hope any of the above can be of use to you, and I'm looking forward to playtesting other versions down the line, see what you change and what effect it has on my experience!
R: even if fixed camera, I think smoothed movement is better!
