The Bubble Tank series offer a unique challenge which makes those games enjoyable. I wouldn't mind seeing a Bubble Tank III. I wonder if there would be a new Bubble Tank?
Bubble tanks does not need a story line. Also, the second one was great, but the third one needs:
Autosave Power Ups Some kind of clear pattern (so that you mostly always now where to go Battle mode A story mode (not a story line), where you complete different bubbles with different challenges.