This game is reminiscent of Robotron. But the similarity is only confined to the firing action.
The basic idea is to blast your way through a series of rooms, each containing a number of nasties. The action is fast and furious and it is quite a challenging game.
The graphics are quite up to standard and highly acceptable for this type of game.
One interesting point is that you can blast a hole in the wall of your current screen without killing all the nasties. However they may be gone, but they are not forgotten. They can actually follow you down the hole that you made and attack from the rear.