Well since you already said this is an early demo I'm only going to say one thing about the graphics: There is a serious clash of art styles. The Title Card looks great but your main character is a pixel art sprite while everything else seems to be watercolor/vector textures.
You can see a clear divide of the background image; it seems like you used a non-repeating sprite.
Gameplaywise:
-Background continues scrolling even when it's game over.
-Collision doesn't always work, I've had instances where character passed through the big trees no problem but gets game over with the small ones.
-Flags which I assume get you points sometimes spawn way to the edge of the screen with hardly any space left for your character to pass through.