Brilliant game mechanic, but easy to "cheat"...
Mr. Driller's obstacles are all in place and must be destroyed... but CAREFULLY!
Imagine a giant stack of, well, colored blocks. Gravity is in full effect, everything is waiting to come down. Four or more of the same color touching will disappear but only if at least one block has just fallen into place. That means a giant agglomeration of red blocks will suddenly "crumble" if you add just one more. If a block is falling it will "stick" to a like color as long as there are less than four stuck together (in which case they disappear, sending things falling again.)
It is important to breathe correctly while engaging in this destruction. The preferred substance is AIR which is scarce and trapped in tanks lightly peppering the brickscape.
It is very rewarding to skillfully destroy everything, but it is also possible to just drill like crazy and hope most bricks disappear before they can squish you. You won't advance very far, but it can be a tempting strategy.
This game feels a bit too difficult with its default settings, but a bit easy with all the enhancements you can buy for Mr.D: more lives, fuller air tanks, shields etc... Characters with specific built-in abilities are unlocked as you progress.
I maxed out my enhancements in order to unlock the characters then toned them back to better appreciate the gameplay, which, is quite nifty. If they took this same mechanic and gave it sophisticated "Lumines" type treatment, I think it would be more popular.