Playing this as a single-player was pretty hard! I got past the first boss, and died to the second. In the waves of the second stage, I was pretty much just trying to avoid getting hit by the bullets more than trying to kill anything.
I liked being able to upgrade the ships. I had some cards that could only go in my hand, but I had no idea what to do with them. They seemed pretty useful, like being able to heal my ships, but I didn't know how to use them :(
The font for the text was kind of hard to read, but the flavor text of the merchants was nice.