I'm going to agree with a lot of other people here, and say that the controls are a little unwieldy. In addition, there isn't any particular reason why JKL should be assigned to those respective colors - they aren't even in the same order as the color wheel on the bottom. (Which I would think would be the obvious way to order them)
It was sort of fun for a while, and I agree that it is nice that you can't accidentally leave a bubble. After a few arenas though, when I didn't change the tank at all, it got sort of repetitive and boring. As others have said, there is no real advantage to being big over being small and nimble, so getting the bubble points is sort of useless if you don't have the corresponding gun points.
Neat, I liked it, I thought that it was pretty intuitive, once you spent a minute or two playing with each level, so the lack of instruction didn't bother me, I didn't really think that they were necessary here.
This is definitely going to be a favourite of mine, I can tell... it's kind of elegant in its simplicity. My only comment is that on your how to play screen the game logo makes it hard to read the text. Also, it might be nice to have a "play again" button on the high score screen after you die, instead of going back to the main menu each time.
Awesome!!
I have to say, I like simon, but I need the sound. I don't think that I would even mind that the puzzle is different each time if there was sound to help me remember.
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 "Bubble Tanks Arenas"){kind=icon}
 "Coil"){kind=icon}
 "Sprout"){kind=icon}
 "Ghoul Academy"){kind=icon}
 "TypingBubble"){kind=icon}
 "Understanding Games: Episode 1"){kind=tracking}
 "Float"){kind=icon}
 "Bridge"){kind=icon}
 "Memory"){kind=icon}
 "Four Second Fury"){kind=icon}
 "Scribble 2!"){kind=icon}
 "Arrival In Hell"){kind=icon}
 "Prehistoric."){kind=icon}
 "Dark Cut"){kind=icon}