Not bad.
The theming with sun and sunflowers, light and dark, it all builds a nice context and theme, the grey background with the yellow flowers is a good way to make them stand out, that I all like.
But there was one thing about it I liked less.. The monster..
There was ok build up, knowing they're always there, and that visual effect when they are close.
But then they themselves show up..
To me at least. They feel less like a big bad that wants to murder me, and more like a gremlin who's after me lucky hearts, only missing them cackling to wind as they run off after poking me.. I'm not quite sure what it is about them but that's the feeling I get looking at them..
Although I'll give you this, in my playtime it happened twice that I was on my last heart running from them, carrying the last flower, and that, that was tense..