This is actually really cool. Reminds me of that helicopter flash game.

I pretty quickly became so OP I could probably deal with an endless solid wall so I got bored and stopped. I think balancing, or even removing, the upgrading would make this a seriously addictive time waster. Adding more types of the explosive boxes seems like it could be fun too.

A bug I noticed is the bullets don't really go where you click because they are not affected by the horizontal camera movement. It doesn't matter once your bullets speed up, but in the early game it's pretty annoying.

I don't like the hold to shoot thing either, should be instant on click with a cooldown. Again, not actually a big deal since you mostly hold the button, but it doesn't feel good.

My impressions:

1. It's fun although a little slow at the start
2. I don't understand where power ups come from although I suspect it's from the blue blocks
3. About a minute in I got so powerful I couldn't even see the obstacles, trivializing the game, and at the big fast bullets seemed to ignore a few blocks
4. I'm used to playing STGs so it feels a little weird not to be able to move left and right

Conclusion:

It's ok, think that with better balancing of the game pace/obstacles/firepower it could  be a great game.