The Tree of Knowledge [challenge/normal/large]

I found the difficulty, once the switch was pulled, nigh impossible, unless I'm totally missing something.  Are we really suppose to be able to jump over the pink spike walkers?  Yeah, I think it needs a little extra on the visual front.  I couldn't figure out why their were no enemies at all, which made the level look way too empty, until I pulled the tongue switch.  In retrospect, I think it is cool, but a little more visually will help keep it from feeling so empty and unfinished.  The background depth layering was almost too subtle to notice, and after seeing the effect several times I finally noticed it by will power alone.  Small faded snakes in the background perhaps?

The level normally shouldn't go beyond Normal / Hard. if a spiky guy goes into a unjumpable position before you can get there, it probably means that you have to try another way. Remember that the info screen said you can hold down and jump to go through thin bridges. I agree that some mid-background details could be good, although it could prove hard to do given how plenty of the tileset seems to be used for the shadows aldready.

Also, i liked that boss battle at the end, the COs and KS+ mechanics certainly make them more fluid and awesome looking than "Shift animations".

1. You could use them like Kraid's claws from the Metroid games or Sakit's platforms from La Mulana (or even Mecha-Birdo's eggs from IWBTG, where you use the vertical mobility they provide to dodge attacks and approach the boss.

2. You could use them to enhance a chase section. Something like Don't Stop Running is limited by the fact that Juni can only move to places where there are platforms; having two-way platforms would make moving up and down a lot freer and safer, making dodge-the-obstacles a lot more fun.

3. You could do something like the time button challenge Talps made for Upper Levels and I Dreamed of the Sky, where a homing spike enemy chases you as you try to push a button. Talps did his with updraughts and the umbrella, but the same thing would also work well with an array of two-way ledges.

Firstly, there's no thud when the stone closes behind you after you beat the boss. Secondly, there's the area with the pool blocked off by four bouncy snakes after activating the dungeon. I had a sneaking suspicion that there was something hidden there and made several attempts at slotting Juni between the upper and lower bouncers, but it turns out it's a void.

Thirdly, the water levels and positions don't change at all. Given how many channels there are, this mechanic seems like something you might have planned to use. I strongly recommend that you do so in another dungeon, if not this one. You could show water in formerly-accessable rooms to suggest the idea of water-powered mechanisms without making the player deal with water level puzzles. This would also make a good way to hide a secret: for example, there could be a way to get back into a room formerly containing water to access the bottom of the pool.

Fourthly, there's the second set of snake heads over water. The highest head is useless and serves only to make the player more likely to die, but it's the only purposeless thing in the whole dungeon. Every other feature is useful at some point, so having the first useless thing be above water is a little irritating: it's out of keeping with the easy/normal tone of the level. Either have more features that are just for show/fun (my preference) or don't have any.

My first major disappointment was the lack of secrets. The temple layout screams about secrets. You've got two-way ledges, hidden passages (like the one after the boss), levers and water channels. What more could you ask for?

The boss is a trifle dull. A patient player never has to take any risks and there's no reason not to be patient. The difficulty doesn't rise smoothly: an incautious player is much more likely to be killed by the three-way spray than by the bouncer. Personally I recommend using liquid drops. If you recolour the ghostly drops to match the temple's water you could use the scenery droplets you already have to give warning for where deadly drops would appear later on in the fight (possibly dripping from the mouths of snake heads on the ceiling). Even better, you could make puddles by making slight hollows in the floor under where the drops appear, making it less safe to fall off in later stages. Doing this would make the challenge significantly higher (but still suitable for a normal level), which seems fitting, given that the boss is usually the hardest part of a dungeon.

You could use them like Kraid's claws from the Metroid games...

That is an example I've thought of many times. The jump-through platforms in KS+ don't move, but Metroid is a source of inspiration for me.

Firstly, there's no thud when the stone closes behind you after you beat the boss.

That happens off-screen, so I'm not too sure it's a good idea.

I had a sneaking suspicion that there was something hidden there and made several attempts at slotting Juni between the upper and lower bouncers, but it turns out it's a void.

Although it is possible to fall between the snakes, invisible slopes make it impossible to reach the void. You should get bounced as soon as you try to move past the lower snakes.

Thirdly, the water levels and positions don't change at all.

Being the Earth temple, I don't think that is appropriate. There is a Water temple later on. I'm not sure how the Temple will work however.

The highest head is useless and serves only to make the player more likely to die, but it's the only purposeless thing in the whole dungeon.

The point of it is to obscure the fact that snakes statues create paths. Without it there I'm afraid players would be more likely to attempt crossing the pool during the maze portion. There are some pointless platforms in the upper galleries, and some snails which you can never use.

My first major disappointment was the lack of secrets.

I love secrets, but I hate missing them. These temples are one-time-visit locations, meaning any secrets you miss inside them are permanently missed. I don't want that to happen to anyone, so there are no secrets in one-time-visit locations. Rest assured, there will be plenty of secrets to find elsewhere.

The boss is a trifle dull. A patient player never has to take any risks and there's no reason not to be patient.

You're right about there not being a reason to rush. It may be a good idea to add those enemies that slowly float towards the player even though walls. Like I've said before though, this boss is supposed to be easy.

There's a section that requires finding a number of puppies and carrying them back (one at a time) to their owner.