Art and music is great. Levels are suprisingly tight. I'm not too hot on "money being spent every second of flight", but it wasn't an issue to me.
Secrets are fairly noticeable, though sometimes robot buddies reveal them by shooting enemies behind the secret walls.
My only complaint would be about the screen resolutions - 2/3 were too small (had to change my screen resolution), while the last one was bigger than my 4k monitor - I guess that's a bug.
But the game is pretty fun, I really liked it.