Great addicting game!
Hi there Ali, don't know if you remember me from Flashkit. First I have to say this is an awesome game, very well polished in every aspect. Second, it is impossible not to compare it to Motherload if you've played it before, and I have... a lot. in fact it's one of my favorite Flash games of all time, and the similarities are quite noticeable. So having that in mind I must say you've improved some things from that one, and that this game stands up to the heat very well.
I liked the fact that you only spend fuel when you move, and when you are beneath the surface, which makes not too stressing. The visual style is very neat and so does the sounds, they fit very well overall.
One thing I also liked is that you designed the game in a way that it makes you drill more sideways rather than going straight underneath, which was something that you could do on Motherload if you knew what was it all about. And that was the best technique to use, going downwards to get to the more pricy minerals faster. With your upgrade system it pushes you to get more of the first minerals in order to go deeper, which I think you managed very well. I must say though, that the upgrades are a bit to high to get after the first ones, but that's not too bad.
I must point too that even when drilling upwards is cool, it makes the game easier, taking the thinking away a bit.
Overall I find the game awesome and very rewarding, got hooked from the first minute. I'm glad that a game like this was done and it is this good, because I love this whole drilling thing a lot. Haven't got too far in the game so I'll see if I find something interesting in the bottom :P Keep up the good work!