Thank you so much for your taking time to write your comprehensive feedback - really appriciate. Makes me happy that you noticed the transitions - I invested a lot to make them as best as I could, for me this was quite important. Sorry for the input issue, it's a nasty race condition that is hard to come by.
When moving is too slow (usually upwards), this can be caused by too wet wings - by the end of 2nd level this "problem" is typically the worst. But when you stay close to the sun in the first part, the effect can be negoiated pretty well - the wings then don't wet so quickly. This is all kind-of intentional (wanted to avoid the "nervous" flappy bird experience) - but I also had these plays where the wings just got too wet - and then some obstacles are just too tough, I can understand your frustration.
Anyways, thanks again for your great feedback. Will also check out your game tomorrow.