As for the concept, I think the idea is solid, but at this stage it needs major reworking
First, I ran into two bugs in a short play session, for example, the "clock out" button didn't work after I died. There's also a lack of feedback when enemies die: no shadows under them and death animations is not emought. In this type of game, weapon feedback and impact effects really matter a lot. Visual tower upgrades are important in this genre, players want to actually see their towers getting stronger.
As for the towers themselves, I liked that there's a good variety to choose from. What I didn't like is the train length limit, I'd love the option to make it longer, and maybe in the future have different maps where you could place two trains, that kind of thing.
Also, towers currently have pretty short attack range, which feels lacking. Enemies spawning from the top and bottom are also way too close to your base's center, which doesn't feel great either.
Settings also don't seem to work properly, I turned off camera shake, for example, but it was still shaking.
As an indie developer myself, I understand this might sound harsh, but I'd rather be completely honest than sugarcoat it :)