Very cool setting and genre. Reminds me of Iconoclast. I really like the poten-boxes. That really brought the whole idea together for me. 

I found the system a bit confusing at first glance, but I think I figured it out. I would make it more clear that going over the goal is also a detriment. I was very confused about why anyone would ever want a negative. When exactly you add your bonus was also a little unclear. It seems like its only the last card played?