An "art" game isn't made by throwing in some somber music over a three-word story. Although the music was good.
First, what is the point of having the player control this boy on a bike? Why is it one of those weird circus bikes instead of a normal one? Is it supposed to symbolize something? When the boy falls off his bike, does it represent the shattering of his fragile heart? Does it have some kind of deep connection to the emotions of love? Not really, no. If you wanted to go with the whole "love is about charging forward blindly and trusting your heart" thing, you should have ramped up the speed by 1.5x, maybe 2x (and extended the horizontal width slightly to compensate). If you wanted it to be more like "love is about finding inner balance and harmony," you could have added some more large cliff drops. As it is now, it's a bit hard to relate the gameplay to any meaningful perspective on love.
Second, the difficulty. There was only one part that was problematic for me, and that was in the 4th part, when there's a really steep downhill. That could be smoothed out a bit. Also, uphill climbs were a drag. Maybe try reducing some of those. More life checkpoints would also help, since it's annoying to go all the way back to the start.
Third, the story. The end didn't really feel rewarding enough, considering how long the game was. And that's about all I can say, since the beginning and the end were the only points with any story. You could have injected story into the gameplay. For example, you could have the balloon constantly flying around on the screen, which would have the added effect of giving the player a concrete, visible goal to reach for. Stuff even as simple as having someone inside a house turning the lights on or off, or having birds flying around in the forest. I get that it's supposed to be a simple story, but that's the beauty of video games: they can add depth to a story not through words, but through little background animations or gameplay elements.