Thanks for the detailed feedback, guert!
First thing’s first. The visuals are great. Although they are reminiscent of Limbo, I like the more coloured approach. The only concern I have is regarding the front trees. These scrolling trees in front of the screen could become partly transparent when the player is placed behind them. It's not a major issue if there are no obstacles or enemies on screen. However, it's always best to always see the avatar.
Agreed. We'll make sure you'll always be able to see the spirit even if a tree is in front of him - we do need the front trees to convey the depth of the scenes.
In the graphic test build, I really liked the freefall. I know it’s not part of the game, but I liked how I took a leap of faith and dropped. As I fell, the colors started to change from hot colors such as red and orange, to light blue. This is something that could be worked nicely into the final game.

A level which is all about free fall is on our list - and we have a nice idea for it

The gravity test build was also interesting. I enjoyed Super Mario Galaxy and the game reminded me of some of its level concepts. As of now, the controls are cool if you’re on a roll but become tough to adapt if you stop. Lemme explain: If I’m running fast, run up a wall and then do a few jumps without stopping, everything is fine. If I stop moving to recalculate a move, it gets a bit weird. However, you don’t have much control over this. I’m simply warning you that, when doing challenges in your level that requires the player to perform athletic moves from one platform to another, gravity switches makes them much harder. It would also be a good idea to iron out your gravity rules early in development so that they become easy for the player to learn. Right now, I don’t know exactly how it works. For instance, if I jump on a wall on which I can climb on later, will the gravity switch right now or not? If I jump near a wall which is a ground for a floating round platform, will I enter the platform’s gravity center or not? Is gravity switch only occurring by walking on certain part of a wall or every one of them? How does wall jump react to these gravity changes? These are all questions the player will want to know in order to learn the game and reach the locations the player desires within the levels.
Gravity is still a major headache for us - making it completely intuitive is hard to achieve. I think most 'casual' people out there never really got Mario Galaxy becasue of that. Everyone here enjoyes Mario Bros Wii much more than Galaxy especially because Gravity is confusing and it's 3d on top of that.
I think we should have an easier time with the gravity concept, but there are a few things left to tackle to make it feel really great.
The temple build is pretty nice too. The comparison to Limbo is pretty much inevitable. You got a game where a silhouette character is running around in a dark forest. What I like about your game is that it feels much more like a classic platformer. It’s nice to be able to control the character with precision and not feel helpless. It’s also a nice to be able to run.

All in all, the controls are nice and well displayed in the temple level; however, the challenges are pretty hard. Not impossible but they take a while to get used to. I suggest that, if you build a sturdy demo for potential investment possibilities, that you have a softer learning curve. Like I said, I know this is an early demo but it’s best to plan this ahead. One thing I’d like to mention is that, by giving a lot of control to the player, the game become much less moody. It’s not a bad thing but it’s best to plan dramatic event accordingly.
The temple is the last level that you can only enter if you have like 70% of the rest of the demo completed. So our hope is that players at this point will not have a super hard time with it. Even though it is still pretty hard - I guess we've all been kinda inspired by Meat Boy and its ultra hard levels

Did you actually manage to get to the big door at the end?
I'm not that concerned about the game being less moody - for us, it's always gameplay first. There is a story in the game for people that like to fully get into it, but we won't force you to do so. Sein works like a poem, every now and then you pick up a snippet of the story and if you put all of them together, you understand what's happening.
The shadow level was also interesting. I lost the shadow a couple of time and it was hard to see both my obstacles and those of my shadows at once but the concept is good and could work pretty well. With a little more work and some polish, this could become quite fun

I think so. I think the shadow level alone could be enough to make a nice little game. VVVVVV was a super polished experience of one idea - in Sein, a mechanic like that will have its own level and we try to bring most of what that mechanic can do into that level and then move on to the next idea. So every single level will have to be an insanely polished, awesomely addictive experience.
I think it'll be super interesting to see how people will react to the story as well. It's hard to make a story work in a Jump 'n Run styled game, but I think we have the right approach. And we won't even force the player to watch stupid cutscenes.
Thanks for all the feedback, guys! Will post more stuff as soon as we get the demo done.