It's awesome... One of the best games I've played so far this jam.
The first two levels were not too difficult, just teaching you the mechanics and strategy. At first, I was a bit confused since I didn't notice the next tile indicator, so I thought the tiles were random. I think the indicator should be given a coloured outline (like the fast forward button) to stand out better. Once I saw the indicator though, I quickly cleared the first two levels.
The third level was way more difficult (and very fun as a result!) compared to the first two, though reading the comments I think I was kinda lucky by beating it on my first few attempts. My strategy was to place a few starting tiles, take a look at the grid, decide on a path the marbles will take to the goal and then spam the remaining area whenever I got unwanted tiles.
I think it would be kind of fun to add a game mode where you weren't allowed to place rails on certain tiles to make the game even more challenging :)
The music and visuals work together with the game's art direction, too. I especially like the music tracks that were chosen, they really fit the game.
I would definitely like to see more levels if you decide to continue developing the game :)