This was quite amazing for a jam game! So many characters. I must say that the collision boxes / duplication of the character when crossing over between the two edges of the screen really got me sploded a lot of times. Sometimes I could see the same character on both edges of the screen, and it was just rather confusing XD Just something to be aware of.
The difficulty curve in my first run of the first level was actually VERY high because I was introduced to only a couple of periodic attackers, rather than any of the OP shooters :D But once I started over it really balanced out most of the time and kept things interesting with depending on which ships you had. Really if the screen-edge duplication hadn't been happening I think I would have just kept on playing. Great job!! ^_^