So, playing this again. You had not fixed some of my issues, I am unsure if you worked on the controls to make it a bit more tight, as I don't remember how floaty it felt, but I will assume right now that it was fixed somewhat.
Further things to consider:
- The background and foreground need some help distinguishing between the two, especially in the train. You could achieve this by dulling the backgrounds colors a bit more, and/or using parallax technics.
- I didn't realize that if you go left, you still look right; which isn't that natural. Especially since you have enemies, that the player might want to fire at to be safe, as they can immediately stop all your progress. I am unsure you you want to handle shooting at different angles or anything, but yeah.
I will say, my skill level for the levels after the boss fight is just not there, I don't normally play this style of game, so bear that in mind I guess. I also normally skip level 3, as I can't do the on the train part well :x
I like the addition of another character though, that was kind of neat. And giving options to the player with how they wanted to handle the thing.
By the way, you are doing self playtests as well, and making sure you can complete the levels you make right? I know that is a common thing people who make tons of levels sometimes forget to do. And will help you distinguish if things are fair challenge or not.