Okay, here's my review.
I think this game's idea is very good, however the execution is rather lackluster.
Not only did I get insanely motion sick due to your whole screen moving with the cannon, but I also didn't know what to do a lot of the time.
There are two main things in this game, the controlling/steering stick and the button that changes the mode from a minigun to some kind of bomb. However, the bomb seemed rather useless. The minigun could kill all the enemies, no problem, and the bomb just had a delay which made it a lot less useful.
I also died multiple times when playing the first time, due to it not being obvious if I'd been hit or not, I also only found out approximately 4 deaths in that the enemies actually come from both sides. The Movement was also slippery, making it almost impossible to turn in time.
I like the game's concept, but the execution is very bad. Due to the motion sickness, I found myself unable to even beat it. I'm not saying that you did a terrible job, don't get me wrong, the game is a lot of fun. However, I was just simply unable to play it for more than 10 minutes or I was going to throw up.