What a beautiful game, lovely music too! I love the way all the greenery is moving, and the jump animation is very smooth - I think it needs some crickets sound effects :)
You mentioned the level is procedurally generated? Very nice, it's completely seamless and I didn't reach any impossible sections (I was a bit worried when I came across the tall tree though).
I am sad I could not take the football with me, maybe you could add a 'kick' button that allows you to punt it upwards a bit to get it over tall things.
I think also it could use some coyote time. Perhaps also a non-pixel perfect camera so it's not so jumpy when changing height slowly.
The letter you wrote made me a bit sad though, that's why I stopped playing, after the barn.