Now THAT'S a good jam game. Surprised you didn't use those 8 extra hours you had - would have been room to put in audio or fix endless mode. If you do the aforementioned suggestions and maybe added a few more waves to the base game this would be a monetizable release and everything! Maybe limit the number of normal breakables you can attach as well - that was a bit overpowered. I loved playing this and I hope you AT LEAST place top 10. Also you can say your guns start calm and orderly but by the end it's a storm of bullets - I came up with that because I wanted to justify bumping your "theme" rating up one more star.
I developed 3 techniques to help myself win: you fill ALL excess grid space with normal breakables. During the game you clear out one side of the enemies and then rush into the clear area and slowly rotate your tank: lets you use 3 times as much armour before core is exposed and have to aim less. During the later stages you can fire at your own center to send a pretty even spread of bullets in all directions.