I played it on the imp, and I really liked it. Tf2 kept crashing (not your fault) so I missed many parts of the game, but from what I did play, I got some feedback:
First, There's not much health. I noticed that especially as an attacker. It's possible that I just didn't notice the health. If so, make it more visible (you can use lighting, overlays, etc), put it in more useful spots, maybe?
The 1st cp was way to easy to cap. Make a bigger distance from it to the BLU spawn?
I loved the underground part before 3rd cp, I think it was executed rather cleverly. Only one problem: the train is silent. And that's dangerous and unrealistic. Think about real life trains, even electric ones,
they still make plenty of noise.