A very simple game but also full of potential. I like the concept and it's already fun playing it.
The biggest issue I have right off the bat is that the controls are a bit odd. In order to jump, at least for me, I had to hold down the W key and also press the space bar.
Even then it didn't work some times and that lead to my death by falling between the rail cars. Movement for left and right are very crisp and feel good, it feels very nice to move around.
The shooting controls are very good and are simple to use, however when 3 enemies rush you at once it feels quite under-powered, especially when you are having a hard time dodging due to the jump issue.
The sound effects are good and fit the game well, and the music is simple but nice.
Finally, the "Menu" and "Play Again" buttons after you die sometimes blend in with the train car colors making them near impossible to see. In my first play through, I died between a red and green train car and sat at the death screen for a minute mashing all the buttons before I figured out that there was something to click on screen.
After I knew about that it was easy to find again, but first time players may be confused.
Overall, I like the concept of the game and I think it's fun, but there are some issues that need to be fixed. Other than that, very nice game and keep up the good work.