Not bad...
A decent time-waster with pretty good graphics, but I have some complaints about it. First off, the drill sometimes goes through rocks it is supposed to be able to break, which can lead to the player getting stuck behind a wall of rocks if he maybe went for some enclosed shells or something. Also, level 9 is almost impossible to get to; I got to level 8, had about 80-85% of my exp bar filled up, then went to the next stage only to find out that my exp bar was emptied. Beating a level getting more than the maximum amount of exp displayed on the "Current" bar brought my total exp up maybe 1-2%, and like hell I'm going to play the same level 50 times just to get the upgrade. The first 8 levels are so easy to get, there's no need for backtracking.
The first time I played this, I managed somehow to get level 15, which then caused me to lose all abilities... I could neither shoot nor use my drill, even though I looked like the first drill incarnation (when the drill is pink). This was a dealbreaker, because I obviously could not kill the turtle boss (or anything beyond it) without the ability to fire my weapon.
The exp bars for each level on the "world map," so to speak, are glitched, as they start at the far left of the screen and reach all the way to the end of the exp box. For later levels, that means you have an orange bar reaching over the majority of the screen.
Overall, not a bad game, but with the glitches I encountered, the super-easy bosses (I killed the first boss before it could even do anything), and with the complete lack of replayability, I'll give you a 7/10.