Haven't played Downwell so no criticism here! Great polish. I really like the subtle detail of the player dude stretching as he falls. Really sells the 'gravity'.
I found something interesting however; I notice that when you die and begin rewinding back to the start, you can still interact with enemies. However, there doesn't seem to be any consequence to this, but I thought it could really add a 'unique' factor. Basically what I imagine Braid would be, if the rewind only affected you and not the world. What kind of gameplay emerges when you hit enemies while rewinding to the start? Could be something worth exploring further.