Really nice game. Fun to play, great visuals and fitting audio! Here is some more detailed feedback:
- The idea of flipping gravity is nice and playing on the top track certainly adds a difficulty level to the game. Although, currently there is no real incentive for the player to use the top track. Because it felt harder and there was no apparent benefit for me to use it I mostly kept on the bottom track. To have the choice to jump to the top track to be meaningful there should be some advantages/disadvantages in the options. Maybe there could be sections where the bottom track is clearly more difficult (or in some cases even impossible) which would encourage (or force) player to jump to top track to succeed in the game.
- Switching lane when there is already an object immediately on the lane you are changing to should not be possible. First two times that this happened I thought that I just missed some obstacle but when I realized what is happening it started feeling unfair. Because player is focusing on the things that are forward on the track it's difficult to see what is directly next to the character. This can lead to situations where the player dies without really even noticing why. The reason of the death could of course be highlighted in some way but the real solution to this (in my opinion at least) would be to prevent track change when the track is blocked. I think most of the games in this genre work that way, so the players are probably expecting it to work that way in your game too.
- Connection to the theme seems a bit superficial. Instead you clearly well followed the other instructions: 1) to make game that could work as a mobile game and 2) that can be competed for score!
- Leaderboard only has scores and no names. It would be interesting to know who has got each score.