I like the level mode's potential. Perhaps make it so you can't run over crops you've already planted? Of course this would require a redesign of all the maps but I think it could be interesting.
The endless mode was confusing, the controls were different which I don't understand the reasoning for. The audio switching channels based on the direction of the tractor was for me very uncomfortable. Overall the sound effects I found to be not very pleasant and I opted to mute the audio.
I really like these kinds of games and with a little creativity I think you can make this a good one! Keep trying and I'm sure you can make something great!