A highscore of 8... nice.
I love the simplicity of the game! Two colors is exactly what we need, with one control to switch them. Nothing more, and heaven forbid if you can make it less.
It works great the way it is, however it was a little slow and laggy on my computer. It might be that the computer isn't too good, but it's only a bit behind modern systems that aren't intended for gaming. For the simplicity of the animation and graphics, it seemed rather odd that it was having trouble with this. This lag ultimately locks me at level 8, though I'm certain if I had smoother performance I'd be able to make it to 10 at least.
That said, performance issues aside, it could use even a little bit more eye-candy. I don't know what exactly, but nothing necessarily interested me in terms of graphical appearance. It'd be nice if the lower levels were actually deeper inside a cave and that the levels progressively changed, so that level 10 is a crystal cave or something!
Next thing, I wish the cubes had a better indicator where the drill "hit" mark is, whether it's a crack, line, whatever, it's a little difficult to gauge when it's safe to switch the drill and when it isn't. This isn't a problem up to Level 5, but at that point, I don't have the split second to think it through, and I have to work on reflex. It'd make it slightly easier while retaining a fairly high skill cap.
As someone before mentions, where is the game over screen? Or animation for a game over or something? It'd be nice to see the drill bit break (from drilling the wrong color) and then it shows a flashy game over screen. Additionally, can the spacebar also reset the game right there, instead of having to click the icon?
Also, can I map the switch key to anything? I'd prefer to use my left click instead.
4.5/5 What you have here is nice, and I'd like to see it improved upon! Will play this again when I can on my gaming system.