Great game, but too easy
The controls/gameplay/graphics/etc are amazing, but the game is far too easy to complete! Even when you get to the final boss, it's just a matter of dodging a few predictable attacks and shooting as quickly as possible to kill it.
Also, I reached the max xp level at something like stage 5 - which was a bit disappointing. There should be enough xp needed to reach the top level so that you can only get the final necessary xp on the last (or in this case second-last) stage. also managed to get over 100% of the "available xp" on one stage, which is clearly not right.
Lastly, the 50% longer drill is more of a handicap than a bonus, since it can get stuck out in front of you, while you bash into a rock.