Decent. A few unpleasant points in the game:
First, it's not mentioned anywhere that you have to use the mouse cursor to collect the points items, so that bit of instruction is lacking.
Second, the fact that the spray of bullets from the basic gun spreads downwards only from the cursor location makes it hard to collect the point items without taking extra shots to the face. Not too bad, given it makes collection of points only somewhat more difficult, but it doesn't 'feel' right to have the spread of shot only hang down from the cursor location.
Third, the acid spray weapon is not in fact an upgrade, it is a downgrade. The loss of the straight bullet flightpath is a horrible hindrance, especially since in order to successfully hit blimps or helicopters with the spray you need to angle the weapon up into the air and thus simply skip on collecting point/money boxes the entire duration of the weapon.
Finally, at no point is it made clear what the sphere robots do- until the twelfth or thirteenth level I had to just skip using the special attack while those were readied because as far as I could figure out they did nothing. It wasn't until that point, where I used them out of desperation in the hope that they would serve some purpose that it finally became apparent that the mini-bots cause large missiles to fall to the ground instead of flying at you. This is not helpful at all as an uncued ability, particularly as the very next time I tried to use them, they wound up doing nothing at all.
That said, it's otherwise a decently fun little thumb-twiddler.