I'll start by saying the transition effects were gorgeous, really liked them.
Visually, I also enjoyed the darkness and the clouds were okay (although they felt like could use a bit more transparency here and there for effects). The heart was also pretty.
The song felt a bit too repetitive after a while and the wing flapping became annoying really quick. The power ups were nice though!
It took a while before the clouds sped up enough to provide some challenge, like around 400 points. The constant flapping plus the slow start take a lot of the replayability in my opinion. One thing I felt, was that when I got the boost power up, it almost became something bad when I got too close to the top of the screen, I could barely see what was coming and then I'd get hammered down by a cloud. Maybe a moving background to give the idea of speed with the darkness advancing behind, while the character remains mostly centered could solve this one? It's quite a lot to change though!
Anyway, I enjoyed my time escaping from the clouds! Does it have an end? I got to almost 500 score.