There's room for improvement

First off, you can include some instructions as to how to play, maybe a tutorial. It doesn't help when you don't know what you're doing, right?

Some upgrades can be to restore health, or something along those lines.

Music can be added for each level (or each time you go back to the game after buying whatever you need). Variations in music is great too.

After being hit, a small invulnerability frame until you can take damage again. If you don't have enough balls to throw at the rocks, it's going to be a major problem since there are many rocks coming at your way and there's no way you can defend in time.

Not too bad

Hey.

Actually kept me playing until I lost (level 9).

Consider adding these into your list of features, if not already:

- On the title screen, change the Textfield, so that the text cannot be selected. Also, try using a font that matche that of the "Play" button, even if you have to remove the Textfield and just draw a custom label yourself. Same with the upgrade screen.

- Better graphics. There are some freeware textures on the Internet you can use for the walls.

- Sound effects.

- A Health power-up, so you can regain health, or add a health powerup "ball". This ball behaves just like the rocks, except that you must let it touch you to regain some health. If you shoot it, you either destroy it, or it turns into a regular rock.

- Slower moving, larger rock, that either (1) takes 2 or 3 hits to destroy; or (2) takes one hit to destroy, but breaks up into 2 smaller rocks.

- At the end of each level, don't just suddenly it. Allow all the currently active rocks to complete, then end the level. I imaging you're either doing each level based of a set amount of time or a certain number of rocks. Either way, once that limit has been reached, don't produce anymore rocks, and wait for all currently active ones to be removed.

- Some additional power-ups to consider:
1) Money power-up. When you collect it, it gives you a nice chuck of money, OR it adds a temporary multiplier to your current gains from shooting rocks.
2) Temporary invulnerability.
3) Temporary speed debuf on incoming rocks.

That's probably enough to keep you busy. (:
Good skill.

______________________
- Ziro out.

Definitely needs polishing.

At least the title was entertaining.

The game's graphics are minimalistic, which wouldn't be a serious issue if you weren't thrown straight into the game without a clue as to what you're doing. The game could seriously use a tutorial, or you could write what you're supposed to do in the description as it took me fifteen seconds to figure out that it was a tunnel and those rocks were hitting me.

There is no sound in the game thus far, and it bored me. However, boring is better than annoying, so if you don't have any good sounds yet, it's a good thing you didn't add the bad ones.

Because of the lack of tutorial, the gameplay was confusing at first, but once you understand what to do, it's pretty straightforward. It's difficult to tell your bouncing angle when you throw your ball(?) against the rocks, though, so you may want to fix that. Another problem is that when the ball gets to the end of the tunnel, it doesn't disappear and return to your inventory so you can throw it again. This left me open to rocks for a solid half-minute, so you may want to implement that. One last thing is that the difficulty curve is kind of steep. Upgrades cost some big money, and you don't get the money fast enough before they start sending three or four rocks down your path.

At this stage of development, the lack of story (or reason for gameplay) is something to be gotten away with, but it is still something to consider.

The game has several problems, but it's still good for a first. You might want to set priority on the gameplay first, and worry about all of the other stuff later.