great game
Well I've played this game for a lot of hours and I really like it. I do have some suggestions though that I hope you'll consider when making IndestructoTank 2.
Probably the biggest problem with the game, is that it's metaphorically challenged. You have a fuel bar, but you have no way to "save fuel." Even if you're being tossed around in the air you're using fuel somehow. So really it's just a timer. The challenge is to rack up as many points as you can within a certain time limit.
But the other problem comes in with the "experience" system. It really makes no sense at all in this game. In RPG games you can imagine your player getting better and better with his sword or magic, allowing him to take on stronger and stronger opponents. But that makes no sense here. You're just bouncing from explosion to explosion. They're really just points.
And if they're really just points, why do you have to wait until you touch ground again to earn them? I'm aware that the number of points depends on the number of combinations you make. But you can calculate that on the fly. For the most part this system doesn't get in the way of game play. Maybe it even makes it more fun. But with the fuel/timer system the way it is, you can blow up in mid-air even though you have enough points to go on to the next level. One time, I barely touched ground with enough points to make it to the very last level. But I blew up WHILE THE GAME WAS COUNTING MY POINTS!!! It's that kind of frustration that makes a person say "Ok, I'm done with this game."
One more suggestion I'd make is to allow the tank to leave the boundaries of the window by a few pixels. Sometimes you should be able to collide with a helicopter or plane just as they're leaving the window. But your tank's movement can't quite reach the edges of the window, so you miss a collision.
Anyway again you've made a great game. I really enjoyed playing it. Looking forward to the sequel.