Never heard of Subway Surfers - it was Temple Run I was inspired by, but i'm sure they will be same sort of thing.
"there is not much challenge" - getting difficulty set for games is really hard and I was being really conscious that I mostly make them too difficult. At the end of each level, difficulty is increased by two random elements between Game speed, Obstacle power, witch speed, horse speed, more obstacles, pumpkins less powerful etc. I made it random to make each game slightly different. But It gets really hard, I thought too quick for a casual game.
The horse changing lanes was going to be independent but in the end for quick coding, due to time restraints and easy catching made it follow the player.
Thanks for playing and the comprehensive review - much appreciated.