I would suggest fixing the slippery mouse controls. Even with the sensitivity set to fast, there's still some kind of "smoothing" applied on the mouse movement that makes it harder to aim at platform.
For the secrets, I think having the collectibles emit some kind of a faint humming noise would make them a little easier to come across. The one and only secret I found was completely by mistake as I had lost my way.
Adding different textures to platformable surfaces will make them a bit easier to discern from walls.
That's all the suggestions I have after playing version 1.0.