I have to admit, I wasn't expecting a lot from this game at first. I've played a lot of mobile games with a similar concept, i.e. fill the level with one line. My main problem with them is that no matter how fun I hope it will be, they're always too simple with no real puzzle element and every level ends up feeling like a chore.
This game, on the other hand, restored my faith in games of this nature. It was refreshing to find myself legitimately puzzling over how best to navigate levels, and the crossover and portal tiles were excellent mechanics that were easy to understand and added a lot to each puzzle. I'm also glad that there weren't any more mechanics than that. I think it was the perfect balance between having one mechanic that can get old after a while and having too many mechanics that overwhelm the player and make the puzzles less enjoyable.
I also appreciated how well the difficulty scaling was done. There weren't many times that I felt like the difficulty level had plateaued or decreased as the game went on, and I felt that all of the game mechanics were introduced gracefully and intuitively.
And finally, I really appreciated that there were keyboard controls. I know I would have likely gotten frustrated if I had to play only by clicking and dragging. I'm not knocking mouse controls or anything! I just personally prefer the accuracy of the arrow keys and I was glad I could use them.
Basically, thanks for making a fun puzzle game with a lot of thought and effort put into each level. It was a good time and I played the whole thing without getting bored or getting too stuck.
Good stuff!